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Nitrogen-limited Cyanobacterial Harmful Algal Blooms in Deal Lake, New Jersey

Jason E. Adolf*1, Katie Saldutti2, Erin Conlon1, Eric Ernst3, Bill Heddendorf3, Sheri Shifren3, and Robert Schuster3

1Monmouth University, Biology Department, 400 Cedar Avenue, West Long Branch, NJ 07764. 2Rutgers, Department of Marine and Coastal Science, 71 Dudley Rd., New Brunswick, NJ 08901. 3NJ DEP, Bureau of Marine Water Monitoring, PO BOX 405, Stoney Hill Rd., Leeds Pt., NJ 08220. *Corresponding author.

Urban Naturalist, No. 57 (2022)

Abstract
Harmful algal blooms (HABs) caused by photosynthetic cyanobacteria (cyanoHABs) have shown expanded impacts in recent decades. Small lakes, reservoirs, and ponds common in highly populated regions are particularly susceptible to cyanoHABs because of high rates of nutrient delivery associated with urbanized watersheds. Deal Lake in Monmouth County, the largest coastal lake in New Jersey, has experienced recurrent HABs in recent years. Here, an analysis of cyanoHAB biomass, nutrient concentrations, and nutrient-addition bioassays (2017–2018) was conducted to address the relationship of cyanoHABs to environmental conditions. Stations within Deal Lake showed differences in median water quality parameters, possibly reflecting different watershed inputs. HAB biomass peaked in late summer in both years, with water temperatures between 77 and 86 °F (25 and 30 °C). Dissolved inorganic Nitrogen (N) peaked in late winter – early spring while organic N peaked in summer. Conversely, dissolved inorganic Phosphorus (DIP) was minimal in late-winter – spring, but elevated in summer during cyanoHABs when pH was also elevated. Nutrient addition bioassays indicated P-limitation in a March experiment, but N-limitation in summer when cyanoHABs were present. Deal Lake summertime cyanoHABs are N-limited, a condition that is reinforced by excess DIP likely coming from autochthonous sources during HAB events. Seasonally elevated water temperatures further reinforce the formation of cyanobacterial HABs in Deal Lake.

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Volume 9, 2022 Urban Naturalist No. 57 Nitrogen-limited Cyanobacterial Harmful Algal Blooms in Deal Lake, New Jersey Jason E. Adolf, Katie Saldutti, Erin Conlon, Eric Ernst, Bill Heddendorf, Sheri Shifren, and Robert Schuster Urban Naturalist The Urban Naturalist (ISSN # 2328-8965) is published by the Eagle Hill Institute, PO Box 9, 59 Eagle Hill Road, Steuben, ME 04680- 0009. Phone 207-546-2821 Ext. 4, FAX 207-546-3042. E-mail: office@eaglehill.us. Webpage: http://www.eaglehill.us/urna. Copyright © 2022, all rights reserved. Published on an article by article basis. Special issue proposals are welcome. The Urban Naturalist is an open access journal. Authors: Submission guidelines are available at http://www.eaglehill.us/urna. Co-published journals: The Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, and Eastern Paleontologist, each with a separate Board of Editors. The Eagle Hill Institute is a tax exempt 501(c)(3) nonprofit corporation of the State of Maine (Federal ID # 010379899). Board of Editors Hal Brundage, Environmental Research and Consulting, Inc, Lewes, DE, USA Sabina Caula, Universidad de Carabobo, Naguanagua, Venezuela Sylvio Codella, Kean University, Union New Jersey, USA Julie Craves, University of Michigan-Dearborn, Dearborn, MI, USA Ana Faggi, Universidad de Flores/CONICET, Buenos Aires, Argentina Leonie Fischer, University Stuttgart, Stuttgart, Germany Chad Johnson, Arizona State University, Glendale, AZ, USA Jose Ramirez-Garofalo, Rutgers University, New Brunswick, NJ. Sonja Knapp, Helmholtz Centre for Environmental Research–UFZ, Halle (Saale), Germany David Krauss, City University of New York, New York, NY, USA Joerg-Henner Lotze, Eagle Hill Institute, Steuben, ME. Publisher Kristi MacDonald, Hudsonia, Bard College, Annandale-on- Hudson, NY, USA Tibor Magura, University of Debrecen, Debrecen, Hungary Brooke Maslo, Rutgers University, New Brunswick, NJ, USA Mike McKinney, University of Tennessee, Knoxville, TN, USA. Journal Editor Desirée Narango, University of Massachusetts, Amherst, MA, USA Zoltán Németh, Department of Evolutionary Zoology and Human Biology, University of Debrecen, Debrecen, Hungary Joseph Rachlin, Lehman College, City University of New York, New York, NY, USA Jose Ramirez-Garofalo, Rutgers University, New Brunswick, NJ, USA Travis Ryan, Center for Urban Ecology, Butler University, Indianapolis, IN, USA Michael Strohbach, Technische Universität Braunschweig, Institute of Geoecology, Braunschweig, Germany Katalin Szlavecz, Johns Hopkins University, Baltimore, MD, USA Advisory Board Myla Aronson, Rutgers University, New Brunswick, NJ, USA Mark McDonnell, Royal Botanic Gardens Victoria and University of Melbourne, Melbourne, Australia Charles Nilon, University of Missouri, Columbia, MO, USA Dagmar Haase, Helmholtz Centre for Environmental Research–UFZ, Leipzig, Germany Sarel Cilliers, North-West University, Potchefstroom, South Africa Maria Ignatieva, University of Western Australia, Perth, Western Australia, Australia ♦ The Urban Naturalist is a peer-reviewed and edited interdisciplinary natural history journal with a global focus on urban areas (ISSN 2328- 8965 [online]). ♦ The journal features research articles, notes, and research summaries on terrestrial, freshwater, and marine organisms and their habitats. ♦ It offers article-by-article online publication for prompt distribution to a global audience. ♦ It offers authors the option of publishing large files such as data tables, and audio and video clips as online supplemental files. ♦ Special issues - The Urban Naturalist welcomes proposals for special issues that are based on conference proceedings or on a series of invitational articles. Special issue editors can rely on the publisher’s years of experiences in efficiently handling most details relating to the publication of special issues. ♦ Indexing - The Urban Naturalist is a young journal whose indexing at this time is by way of author entries in Google Scholar and Researchgate. Its indexing coverage is expected to become comparable to that of the Institute's first 3 journals (Northeastern Naturalist, Southeastern Naturalist, and Journal of the North Atlantic). These 3 journals are included in full-text in BioOne.org and JSTOR.org and are indexed in Web of Science (clarivate.com) and EBSCO.com. ♦ The journal's staff is pleased to discuss ideas for manuscripts and to assist during all stages of manuscript preparation. The journal has a page charge to help defray a portion of the costs of publishing manuscripts. Instructions for Authors are available online on the journal’s website (http://www.eaglehill.us/urna). ♦ It is co-published with the Northeastern Naturalist, Southeastern Naturalist, Caribbean Naturalist, Eastern Paleontologist, Eastern Biologist, and Journal of the North Atlantic. ♦ It is available online in full-text version on the journal's website (http://www.eaglehill.us/urna). Arrangements for inclusion in other databases are being pursued. Cover Photograph: Summertime cyanobacteria discolor Deal Lake waters at the Jersey Shore. Photograph © Jason Adolf. 1 1Monmouth University, Biology Department, 400 Cedar Avenue, West Long Branch, NJ 07764. 2Rutgers, Department of Marine and Coastal Science, 71 Dudley Rd., New Brunswick, NJ 08901. 3NJ DEP, Bureau of Marine Water Monitoring, PO BOX 405, Stoney Hill Rd., Leeds Pt., NJ 08220. *Corresponding author: jadolf@monmouth.edu. Associate Editor: Juan Carlos Villarreal Aguilar, Department of Biology, Laval University. Nitrogen-limited Cyanobacterial Harmful Algal Blooms in Deal Lake, New Jersey Jason E. Adolf *1, Katie Saldutti2, Erin Conlon1, Eric Ernst3, Bill Heddendorf 3, Sheri Shifren3, and Robert Schuster3 Abstract - Harmful algal blooms (HABs) caused by photosynthetic cyanobacteria (cyanoHABs) have shown expanded impacts in recent decades. Small lakes, reservoirs, and ponds common in highly populated regions are particularly susceptible to cyanoHABs because of high rates of nutrient delivery associated with urbanized watersheds. Deal Lake in Monmouth County, the largest coastal lake in New Jersey, has experienced recurrent HABs in recent years. Here, an analysis of cyanoHAB biomass, nutrient concentrations, and nutrient-addition bioassays (2017–2018) was conducted to address the relationship of cyanoHABs to environmental conditions. Stations within Deal Lake showed differences in median water quality parameters, possibly reflecting different watershed inputs. HAB biomass peaked in late summer in both years, with water temperatures between 77 and 86 °F (25 and 30 °C). Dissolved inorganic Nitrogen (N) peaked in late winter – early spring while organic N peaked in summer. Conversely, dissolved inorganic Phosphorus (DIP) was minimal in late-winter – spring, but elevated in summer during cyanoHABs when pH was also elevated. Nutrient addition bioassays indicated P-limitation in a March experiment, but N-limitation in summer when cyanoHABs were present. Deal Lake summertime cyanoHABs are N-limited, a condition that is reinforced by excess DIP likely coming from autochthonous sources during HAB events. Seasonally elevated water temperatures further reinforce the formation of cyanobacterial HABs in Deal Lake. Introduction Harmful algal blooms (HABs) caused by cyanobacteria (cyanoHABs) in freshwater systems are a growing phenomenon worldwide that impacts ecosystems, economies, and people (O’Neil et al. 2012). Harmful impacts of cyanoHABs can include ecological disruption through formation of dense surface accumulations that block sunlight from reaching benthic communities; potential production of toxins that can affect humans, pets, and domestic animals; as well as production of taste and odor compounds that impact municipal water supplies (Paerl and Otten 2013, Watson et al. 2016). The proliferation and expanding impacts of cyanoHABs around the world have been linked to nutrient over-enrichment, climate change and changing use of aquatic environments, but the details behind the nutrient-climate-cyanoHAB connection can differ from place-to-place, and over time within a given system (Chapra et al. 2017, Griffith and Gobler 2020, Hallegraeff et al. 2021, Paerl 2018, Paerl and Huisman 2008, Paerl and Otten 2013, Paerl and Paul 2012). For instance, highly urbanized watersheds have complex and sometimes novel patterns of nutrient cycling and delivery to small ponds, retention basins, and lakes that are often found in these environments (reviewed in Carey et al. 2013). The combination of heavy rainfall events and highly urbanized watersheds has been shown to lead to severe water quality issues for lakes (Olds et al. 2018, Salerno et al. 2018, Wei et al. 2020). CyanoHABs in urban waterbodies are of particular concern because of the 2022 Urban Naturalist 57:1–19 Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 2 potential for toxicity coupled to the high surrounding population densities (de la Cruz et al. 2017, Waajen et al. 2014, Lewitus et al. 2003). Like all phytoplankton, cyanobacteria require both N and P as major nutrients for growth, and are favored by particular sets of physical conditions (e.g., light, temperature, turbidity; Paerl and Huisman 2008). However, determining the relative role of N vs. P in driving cyanoHABs is complex due to factors including different species’ nutritional strategies (Paerl 2018, Paerl and Otten 2013) as well as seasonal differences in nutrient availability (Chaffin et al. 2018a, Xu et al. 2010). For example, cyanobacteria with the ability to fix atmospheric N2 may have an advantage in N-limited water bodies due to their ability to access the pool of atmospheric N2 that is unavailable to most other species of phytoplankton, but the existence of other factors (e.g, water temperature) can sometimes result in dominance of non-N-fixers in N-limited lakes (reviewed in Paerl and Otten 2016). Further, different forms of fixed N (e.g. nitrate, ammonium, or urea) have been shown to be preferred by different species of phytoplankton leading to changes in natural lake phytoplankton community structure (Trommer et al. 2020). Watershed inputs of P have often been implicated in cyanoHAB formation, particularly as “legacy loading” to lake sediments that integrates years of past inputs (Sharpley et al. 2013, Randall et al. 2019). The tendency for HAB cyanobacteria, such as Microcystis spp., to have higher optimal growth temperatures (≥ 77 °F (25 °C)) than competitor chlorophytes and diatoms is often cited to link their expansion to climate change (Paerl and Huisman 2008). However, climate-related changes in regional rainfall and hydrology affecting nutrient transport to lake ecosystems are also important (Chapra et al. 2017). The complex interactions between N, P, climate, growth and toxicity of cyanoHABs (Gobler et al. 2016), underscores the need for comprehensive dual-nutrient management strategies that include attention to N and P (Paerl 2018). New Jersey is home to ~1700 lakes, some of which are located along the densely populated New Jersey shore, and are referred to as coastal lakes. Historically, many of these coastal lakes had a connection to the Atlantic Ocean, and some remain connected albeit through engineered structures that run beneath streets and beaches in highly urbanized or developed watersheds. Coastal lakes traditionally supported a wide range of uses, including spawning grounds for anadromous fishes, swimming, fishing, and boating (Tiedemann et al. 2009). Presently, New Jersey’s coastal lakes are beset with various water quality impairments (Tiedemann et al. 2009), including but not limited to HABs, that preclude state certification for primary contact (e.g. swimming). Deal Lake in Monmouth County, New Jersey (NJ) is the state’s largest coastal lake. The watershed of Deal Lake is highly urban/suburban, and stormwater runoff has been identified as a major source of sediment, nutrient and microbial pollution to the lake (Tiedemann et al. 2009). Residents of the area value Deal Lake for its recreational boating and fishing opportunities, and as a greenspace and wildlife refuge amidst the densely populated region in which it exists. Understanding the relationship between nutrients and HABs in Deal Lake is necessary for effective management and mitigation efforts that will ensure ongoing safe access to this environment by people, pets and wildlife alike. Summertime cyanoHABs have led to regulatory actions restricting the use of Deal Lake by the public. The objective of this study was to analyze time series of water quality, nutrients, and indicators of cyanobacterial biomass to identify relationships between these parameters, and to gain insight into the relationship between watershed nutrient loading and HAB occurrence. Additionally, nutrient addition bioassays were conducted in 2018 to determine whether N or P was limiting cyanobacterial biomass. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 3 Materials and Methods Field Site Description, Sampling, and Nutrient Analyses Deal Lake is the largest coastal lake in the state of NJ, with a total surface area of 155 acres (0.63 km2), average depth of 1.8 m, a watershed area of 4400 acres (17.8 km2) that is classified as “highly urbanized” (Souza 2011), and a trophic status classified as “eutrophic” by previous investigations (Tiedemann et al. 2009). Seven NJ municipalities border Deal Lake with a combined population of approximately 70,000. Deal Lake is characterized by an eastward main basin adjacent to the Atlantic Ocean coastline that tapers to multiple tributary “arms” to the west (Souza 2011; Fig. 1). The lake remains connected to the Atlantic Ocean via a flume gate used to regulate lake level, as well as to allow migratory fish movements into and out of the lake (Souza 2011). Deal Lake’s main basin has a volume of 0.9 × 106 m3, and receives annual inputs of 8.1 × 106 m3 from tributaries and 1.9 × 106 m3 from stormwater annually (Souza 2011). Fig. 1 shows the location of sampling stations on Deal Lake. Samples were taken from the surface using a 1-liter bottle approximately bi-weekly to monthly, with fewer samples in winter. Lakes were accessed from shoreline or bridges, and Secchi depth was measured in situ along with conductivity, temperature, and dissolved oxygen (YSI Pro 2000 multiparameter probe). Figure 1. Deal Lake and sampling locations. Deal Lake station number used in subsequent Figures is the final digit in each station code. Wanamassa Pt. and Comstock St. are locations of nutrient addition bioassays. “Primary” and “supplemental” stations are NJ DEP designations referring to requirements for cell counting within two weeks, or at a later date, respectively. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 4 Chemical Analyses 1-L acid washed amber bottles were used to collect surface water samples for nutrient analysis, pH, and chlorophyll a analysis in the Certified Chemistry Lab at the NJ Department of Environmental Protection (DEP) Bureau of Marine Water Monitoring. Ammonia, Orthophosphate, Nitrate + Nitrite, Total Phosphorus, and Total Nitrogen were analyzed on a SEAL AA3 segmented flow analyzer following EPA and USGS methodologies. An alkaline persulfate digestion was performed on the samples to oxidize all the forms of phosphorus and nitrogen prior to analysis for the Total Phosphorus and Total Nitrogen analysis. The pH was determined on a Hach 440d multimeter with an IntelliCal PHC101 pH probe. The probe had a 3-point calibration with pH buffers at 4, 7, and 10. The chlorophyll a was determined by filtering the sample through a 1.85 in (47 mm) glass fiber filter, placing it in 10 mL of a solution of acetone, dimethyl sulfoxide (DMSO), and water; 54%, 40%, and 6% respectively by volume, and then placing it overnight in the freezer at 4 °F (-20 °C) for extraction. It was then analyzed on a Beckman Coulter DU730 UV/Vis Spectrophotometer. Readings were taken before and after acidification and entered into the following equation, Chl a (μg L−1) = {[26.7 × (664b − 750b) – (665a – 750a)] × 0.01} / [(V2 × 2.54) ]} × 1000 where a = Post-acidification reading; b = Pre-acidification reading; V2 = volume of sample in liters; L = light path length or width of cuvette (2.54 cm). Microcystin concentration was measured by NJ DEP using ELISA assays (Abraxis p/n 520011) according to manufacturer’s protocols including freeze-thaw cycles for cell lysis. Hourly rainfall data were retrieved from http://njdep.rutgers.edu/rainfall/ for station RABCH006, which is located at the eastern end of Deal Lake. Nutrient Addition Bioassays For each bioassay experiment, either 12 or 24 acid-washed 1-L cubitainers (4 or 8 treatments in triplicates, respectively) were rinsed and filled with 800 mL Deal Lake water, and incubated in the lake, in a submerged PVC enclosure covered with 1 layer of black fiberglass screening for 4–6 days. Nutrient stocks for nutrient amendments were purchased from the National Center for Marine Algae and Microbiota at Bigelow Laboratory for Ocean Science (East Boothbay, ME, USA). Nutrients were added in excess relative to typical Deal Lake concentrations, a strategy commonly used in nutrient addition bioassays (Downing et al. 1999), and suited to the goal of identifying the limiting nutrient. Treatments included addition of nitrogen (100 μM NO3, or 1,400 μg N L−1), ammonia (100 μM NH4, or 1,400 μg N L−1), and phosphorous (6.3 μM PO4, or 195 μg P L−1) individually, and combined in Redfield ratio N:P requirements (16:1 molar). Confirmation of initial nutrient concentrations following amendments was made by analyzing a subset of samples on a 9500 Photometer (YSI) according to manufacturer’s instructions for each analyte. Starting conditions for phytoplankton biomass and water temperature are shown in Table 1. During the bioassays, samples were taken daily to monitor growth, and ensure no catastrophic crashes occurred before the final sample was taken. A Turner Designs handheld Cyanofluor was used in this experiment to detect and measure phycocyanin fluorescence (PC), a pigment-based proxy for cyanobacterial biomass. Qualitative analysis was performed by microscopy of pooled replicates from each treatment preserved in Lugol’s iodine (5% final by vol.) solution. Boxplots were produced comparing in vivo fluorescence (IVF) measurements at Tf relative to the control. ANOVA analysis for statistical significance (p < 0.05) was used to analyze results. Phycocyanin fluorescence (PC) has been shown to provide useful indices for tracking changes in cyanobacterial biomass (Hodges et al. 2018, Pasztaleniec et al. 2020, Chaffin et al. 2018b), but still requires ground-truthing to cell measurements. Phycocyanin fluorescence was measured with the Turner Designs CyanoFluor. It was ground-truthed to four cell count sample Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 5 1A Ocean Ave 8/27/2018 245,000 0.16 101A N. Wanamassa Dr 8/27/2018 243,000 0.12 102A Sunset Ave 8/27/2018 205,000 0.1 103A Westra St 8/27/2018 51,000 0.01 104A Corlies Ave 8/27/2018 38,000 0 105A Main St 8/27/2018 727,000 0.15 1A Ocean Ave 8/16/2018 3,200 0.26 101A N. Wanamassa Dr 8/16/2018 15,000 0.13 102A Sunset Ave 8/16/2018 2,000 0.12 A Wickapecko Dr. 8/16/2018 n.p. 0.05 B Ridge Ave 8/16/2018 n.p. 0.01 103A Westra St 8/16/2018 11,800 0.1 104A Corlies Ave 8/16/2018 21,200 0.06 105A Main St 8/16/2018 12,400 0.19 1A Ocean Ave 8/2/2018 >20,000 1.88 101A N. Wanamassa Dr 8/2/2018 >20,000 0.92 102A Sunset Ave 8/2/2018 >20,000 0.82 A Wickapecko Dr. 8/2/2018 n.p. 0 B Ridge Ave 8/2/2018 n.p. 0 103A Westra St 8/2/2018 12,500 0.27 104A Corlies Ave 8/2/2018 n.p. 0.36 105A Main St 8/2/2018 >20,000 1.47 1A Ocean Ave 7/23/2018 >20,000 0.7 Psuedanabaena, Merismopedia Aphanacaphasca, Psuedanabaena, Merismopedia Aphanacaphasca Gleocapsa Gleocapsa, Aphanacaphasca Aphanocapsa, Psuedanabaena, Merismopedia Psuedanabaena, Merismopedia, Raphidiopsis Psuedanabaena, Raphidiopsis Merismopedia ---- ---- Merismopedia, Aphanocapsa Psuedanabaena, Merismopedia, Raphidiopsis, Aphanocapsa Psuedanabaena, Merismopedia, Raphidiopsis, Planktothrix Oscillatoria, Psuedanabaena, Merismopedia, Raphidiopsis Psuedanabaena, Merismopedia Raphidiopsis Psuedanabaena, Merismopedia ---- ---- Merismopedia ---- Merismopedia, Aphanocapsa Raphidiopsis Table 1. Cell and toxin sampling (2018) during Deal Lake bloom. n.p. = not present. Site Location Date Cell count (cells/ml) Microcystins (μg/l) Dominant these taxa Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 6 sets obtained from the summer of 2018, which included water samples taken from: 1) a Secchi Dip event occurring in different coastal lakes on July 19th, 2) a bioassay done in Deal Lake on July 3rd, 3) two bioassays completed in Deal Lake on July 3, and 4) Deal Lake samples taken throughout the summer. These datasets contained in-vivo-fluorescence readings from a handheld Cyanofluor (Turner Designs), and had corresponding samples preserved in 5% final (by volume) Acid Lugol’s iodine solution. One milliliter of these samples was taken after the bottle was inverted and placed in a gridded Sedgewick Rafter Counting Chamber. These chambers were left alone to settle for ten minutes, and then examined on a Nikon Diaphot 300 Inverted microscope. Each sample had five grids counted for three different types of cyanobacteria genera that were dominant: Microcystis, Merismopedia, and Pseudanabaena. Microcystis and Merismopedia were counted as “natural units”. They presented as clumps or sheets of cells, respectively, and Pseudanabaena was counted as trichomes. Scatterplots were made comparing total cyanobacterial cell counts to PC readings. The relationship between total cyanobacterial cells (per mL) and phycocyanin fluorescence (RFU), based on this analysis, was: Total cyanobacterial cells per mL = 0.0024*PC + 17.198 (r2 = 0.38, p < 0.001) For confirmation of bioassay results based on fluorescence, cell counts were performed on pooled replicates of treatments from the starting timepoint (T0) to the end of the experiments. Cluster Analyses of Stations To address whether the nine stations sampled on Deal Lake (Fig. 1) differ from each other based on water quality measurements, a cluster analyses was performed using the “cluster” package in R, and visualized using package “factoextra” with fviz_cluster and ggparcoord functions. Cluster analysis is an exploratory statistical methodology that looks to group cases (e.g., stations) into groups within which stations are more similar than stations are among different groups based on some set of properties (e.g., median water quality parameters over a specified time period). Partitioning around means (PAM) clustering was used as this is a version of the general K-means clustering method that is less sensitive to outliers (i.e. more robust). Data from springs and summers of 2017 and 2018, when the water temperature was >57 °F (14 °C), was used because station #1 was not sampled outside this sample range, and otherwise would have been excluded from the analysis. All water quality parameters were summarized as median values by station, and used as input to calculate distance measures (function fviz_dist), determine optimal number of clusters (function fviz_nbclust), and to perform PAM clustering (function pam). Results Rainfall The Deal Lake rain gauge recorded 46 in (1168 mm) of rain in 2017, and 61 in (1550 mm) in 2018. The timing of rain differed between years, with January–March showing similar accumulations, March–July higher accumulations in 2017, and September–December higher accumulations in 2018 (Fig. 2 and inset). Generally, 2017 was wetter earlier (March–July), and 2018 was wetter later (August–December) in the year (Fig. 2 inset). Water Quality Parameters by Stations and Cluster Analyses Examination of water quality parameters by station (Fig. 3) suggested differences that were subsequently supported by PAM cluster analyses (Fig. 4). Water temperature (Fig. 3A) was the only WQ quality parameter not showing a significant difference among sites. Stations 4A and 4B tended to stand out as different from the other sites for most parameters. Sites 4A and 4B, in Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 7 the southwest arm of Deal Lake (Fig. 1), had lower median Chl a (Fig. 3F) specific conductivity (Fig. 3B), pH (Fig. 3C), D.O. (Fig. 3E) TP (Fig. 3H), PO4 (Fig. 3L) as well as organic N and P (Fig. 3M, N) than other stations. These same stations (4A and 4B) also had higher median DIN (Fig. 3I, J, K), DIN:DIP (Fig. 3O), and TN:TP (Fig. 3P) relative to other sites. Likewise, PAM cluster analysis put stations 4A and 4B into a separate group (cluster 2) from the rest of the stations (Fig. 4A) based on elevated median DIN, TN, TN:TP, and DIN:DIP (Fig. 4B), consistent with an abundance of unincorporated DIN at these sites. Water Quality Time Series As a result of the cluster analysis, stations 4A and 4B were excluded from the time series analysis presented here. Water temperature minima occurred between December and Feb (Fig. 5A), with the lowest recorded average temperature of 36.5 °F (2.5 °C) occurring Dec 13, 2017, followed by averages of 39.7 °F and 43.9 °F (4.3 °C and 6.6 °C), recorded March 27, 2017 and March 14, 2018, respectively. Water temperature maxima occurred between July and September (Fig. 5A), with the highest recorded average temperature of 87.4 °F (29.3 °C) recorded August 9, 2018, followed by 84.4 °F and 83.3 °F (29.1 °C and 28.5 °C) on July 13 and 18, 2017, respectively. Lake pH was elevated in summer, and lower in winter. Average lake pH minima were ~6.5– 7.5 in the December through March, and then elevated at 8.0–10.0 between June and September (Fig. 5B). Lake average dissolved inorganic nitrogen (DIN) was elevated between February and May, with station averages in the 600–1045 μg L−1 range (Fig. 5C). The eight highest DIN values (>1000 μg L−1) were associated mostly (5 of 8 observations) with station 4, located in the southwestern arm of the lake, but also stations 2, 6, and 7. Elevated values tended to occur in March (5 of 8 observations), but three of the station 4 elevated DIN values were recorded in May, June, or August. The DIN was composed of 59±18.1% NH3 during these elevated times. Lower values of DIN occurred between July and October, with lake average Figure 2. Hourly rainfall, 2017 – 2018. Retrieved from http://njdep.rutgers.edu/rainfall/ station RABCH006, located near station 2 on the site map. Inset graph shows annual rainfall accumulation curves for each year. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 8 Figure 3. Box and whisker plots comparing water quality parameters by station. Horizontal line at the center of each box is the median, while the bottom and top of the box are the 1st and 3rd quartiles, respectively. Whiskers extend to 1.5 × the interquartile range. Heavy black points in line with the whiskers are outliers. Jitter (red) shows individual sample values. Figure 4. Cluster analysis of stations based on median water quality parameters. A. Clustering of stations determined by PAM algorithm, showing stations 4A and 4B separate from the others. B. Plot showing standardized values of parameters by group. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 9 values between 3.4 and 28.5 μg L−1, with the exception of some values recorded at station 4 as mentioned above. During these times DIN was 75±14.2% NH3. Lake average organic N varied from ~500 μg L−1 in the winter and spring to ~1500–2200 μg L−1 in the summer and early autumn (Fig. 5D). Figure 5. Physical/chemical parameter time series measured in Deal Lake. Different symbols represent individual station values for each sampling date. The line connects station averages (not shown) for each sampling date. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 10 Lake average DIP tended to be below 25 μg L−1 in winter and spring, and 50–100 μg L−1 in summer, with anomalously high values recorded at station 5 located in the northwest arm of the lake in August 2017 (Fig. 5E). A similar pattern was seen for organic P, with winter minima and summer maxima (Fig. 5F). Lake average DIN:DIP (mol) (Fig 5G) peaked above 100 in late winter and spring, and was low in summer, dropping to <1 on nine occasions recorded in July, August and September. Lake average organic N:P (Fig. 5H) tended to peak at ~50 between July and November, and was lowest at ~25 in March–April. Regressions of Chl a on Nutrients Cyanobacterial-dominated phytoplankton blooms were observed in both years, tending to occur between July and October, with a larger bloom detected in 2017 compared to 2018 (Fig. 6A). A subset of samples (n = 55) measured for both Chl a and phycocyanin show a strong correlation (R = 0.64, p < 0.05) between these two parameters, consistent with cyanobacteria being the dominant phytoplankton during high biomass periods. The highest Chl a values were associated with lower DIN values (Fig. 6B). Organic N increased linearly with Chl a (Fig. 6C), explaining 76% (p < 0.001) of the variability. DIP increased linearly with Chl a (Fig. 6D) explaining 58% of the variability (p < 0.001). Organic P increased linearly with Chl a, but was weakly related (Fig. 6E). The ratio of organic N:P was not significantly related to Chl a (Fig. 6F). Deal Lake Microcystin Measurements Measurements of Deal Lake microcystin concentrations made by NJ DEP and Monmouth County Department of Health (MCDH) during the 2018 bloom show relatively low levels consistently below guidance levels of 3 μg L−1 despite cell numbers that approach 104–106 μL−1 (Table 1). Toxin levels measured early in the bloom tended to be higher than those measured later in the bloom despite elevated cell numbers reported later in the bloom. Nutrient Addition Nioassays Nutrient addition bioassays were performed on Deal Lake water on three different dates in 2018. The earliest bioassay performed on Deal Lake in 2018 was March 24–28, with To Chl a levels of 9 μg L−1 (Table 2). In this bioassay P was determined to be the limiting nutrient of a chlorophyte and diatom dominated phytoplankton community based on increased Chl and PC over the control and N treatments (Fig. 7A., 7B.). The May 31 bioassay was performed at a time when To Chl a biomass was 68 μg L−1 (Table 2). Chl and PC values did not significantly differ from the control (p = 0.112) (Figs. 7C., 7D.). Microscopic analyses of these samples showed predominant flagellates and diatoms with some cyanobacteria present. July 3 bioassays at Comstock St. and Wanamassa Pt. had To Chl a levels of 67 and 147 μg L−1, respectively (Table 2). These bioassays show a strong and significant response to nutrient addition in both PC and Chl values, especially treatments containing NH4 (Fig. 7E–H). Qualitative analysis of pre- Table 2. Starting phytoplankton biomass (Chl a) and water temperature conditions for in-lake nutrient bioassays. The Mar 23 bioassay was performed at station 4A. May 31 and Jul 12 bioassays were performed at Wanamassa Pt. For Jul 3, ‘cs’ refers to Comstock St. and ‘wp’ refers to Wanamassa Pt. as locations of the bioassays. Mar 23 9 7–8 May 31 68 19–20 Jul 3_cs 67 25–29 Jul 3_wp 147 25–29 Jul 12 85 27–28 Bioassay Start Chl a (μg L−1) Water temp. (°C) Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 11 served samples indicated three dominant cyanobacteria types Microcystis, Pseudanabaena and Dolichospermum, with relatively fewer flagellate and diatom species present compared to the May 31 bioassay. The July 12 bioassay had a T0 Chl a value of 85 μg L−1 (Table 2), and showed nitrogen limitation again (Fig. 7I, J). The PC growth in this experiment responded strongly and significantly to all nitrogen containing treatments (p < 0.001), while total biomass of Chl did not respond significantly to any single treatment. Microscopic examination of pooled replicate samples from the June 28 bioassays at both sites showed dominant Micro- Figure 6. A. Chl a time series in Deal Lake. Different symbols represent individual station values for each sampling date. The line connects station averages (not shown) for each sampling date. B. – F. Scatterplots and regressions of Chl a on nutrient parameters. Results of simple linear regression analyses are shown on each graph where relevant. Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 12 cystis, Pseudanabaena, and Mersimopedia that showed increases in abundance similar to that seen in fluorescence measurements. Cell counts in the July 12 pooled replicate samples (Fig. 8C) did not reflect fluorescence measurements as much in terms of total cell counts, but did show a response of Microcystis to treatments containing ammonium. Discussion Deal Lake, the largest of New Jersey’s coastal lakes, was loaded with DIN during the winters observed here, followed by transformation of DIN to organic N (in the form of phytoplankton including HAB biomass) over the summer growing season. Meanwhile, DIP remained low in winter, but increased in the summer in the presence of high cyanoHAB biomass. Consequentially, the nutrient limiting phytoplankton biomass shifted from P in winter and spring to N in summer when HABs predominated. Further, water temperatures above 77 °F (25 °C) typified Deal Lake in summer, and likely contributed to the observed cyanoHABs. These patterns have important implications for lake management and rehabilitation. Spatial Variability Within Deal Lake The groupings of stations revealed by examinations of water quality parameters (Fig. 3) and cluster analyses (Fig. 4), based on elevated levels of DIN at stations 4A and 4B, are consistent with a significant source of DIN being present in the southwest arm of Deal Lake. While determining the source of this DIN was beyond the scope of this study, at least two possible sources of this nitrogen are considered: a golf course, and a historical landfill (presently the site of a mall) located adjacent to the arm of the lake containing these stations. A review of nutrient export from Figure 7. Boxplots comparing treatments to the control at the bioassay endpoint. A. Mar 2018 Chl, B. Mar 2018 PC, C. May 2018 Chl, D. May 2018 PC, E. Jun 2018 Chl (location), F. Jun 2018 PC (location), G. Jun 2018 Chl (location), H. Jun 2018 PC (location), I. Jul 2018 Chl, J. Jul 2018 PC. Treatment codes are N= nitrate; P = phosphate; Am = Ammonia. In each graph, treatments with different letters were significantly different (p < 0.05) by ANOVA post-hoc test (Tukey). Treatments on the x-axis are coded C (control), N (nitrate), P (phosphate), NP (nitrate + phosphate), AmN (ammonia + nitrate), AmP (ammonia + phosphate), AmNP (ammonia + nitrate+phosphate). “n.s.” indicates non-significant ANOVA Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 13 Figure 8 Comparisons of dominant taxa counts (MC = Microcystis, MP = Merismopedia, PA = Pseudanabaena) from pooled replicates for nutrient-addition bioassays from A. Counts are in “natural units” (NU). A. June 2018 (Comstock St)., B. June 2018 (Wanamassa Point), and C. Jul 2018 (Wanamassa Point). Treatments on the x-axis are coded C (control), N (nitrate), P (phosphate), NP (nitrate + phosphate), AmN (ammonia + nitrate), AmP (ammonia + phosphate), AmNP (ammonia + nitrate + phosphate). golf courses found “reasonably low” export from such systems, but emphasized the potential for wide ranging variability depending on site specific soil, rainfall, and best management practices (Bock and Easton 2020). Landfill leachate can also be highly variable depending on the age and regional climatology of the facility, but DIN is identified as a common leachate (particularly as reduced ammonia) along with alkaline pH and elevated conductivity (Luo et al. 2020). Stations 4A and 4B do show elevated ammonia, consistent with landfill leachate, but also elevated nitrate, relatively acidic pH, and low specific conductivity compared to other sites. While stations 4A and 4B appear to be associated with a source of DIN to Deal Lake, further study is needed to identify the source of such nutrients. Seasonal Cycle of Nutrients in Deal Lake Deal Lake was loaded with DIN over the winters when water temperature and cyanoHAB biomass in the lake was generally low. The watershed of Deal Lake is highly urbanized (78.1%) with a high proportion of impervious surfaces (32.2%), making the lake susceptible to stormwater runoff (NJAES 2019). Urban stormwater runoff is a known source of N and P to lakes and coastal waters in many locations (Taylor et al. 2005, Silva et al. 2019). It is a very likely source of winter DIN loading, although specific characterization of the chemical composition of Deal Lake stormwater runoff has not been done. It is interesting to note that in 2017, when heavier Deal Lake blooms were observed, heavier rainfall occurred before (March–July) the HAB-season compared to 2018 when rainfall was greater after (Sept–Dec) the HAB season (Fig. 2). Due to anthropogenic climate change, NJ has seen an 8% increase in precipitation over the past decade, including an increase in extreme precipitation events (>2 in. (51 mm) in a day), Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 14 and similar changes in NJ precipitation are expected to occur through the second half of the 21st century (Runkel et al. 2017). Together, these observations suggest that stormwater runoff will continue to be a major issue contributing to cyanoHABs in Deal Lake. Characterization and management of urban stormwater runoff, as well as tracking the timing of rainfall, should be a priority in the context of cyanoHAB mitigation for Deal Lake. The conclusion that Deal Lake shifts from winter P-limitation to summer N-limitation is supported by nutrient addition bioassays performed in 2018 as well as by nutrient time series throughout the study. Similar patterns of seasonal shifting from P- to N-limitation upon the onset of cyanoHABs have been made by Xu et al. (2010) and Paerl et al. (2015) in Lake Taihou, China, as well as Chaffin et al. (2018a). Nutrient addition bioassay results suggest a temporal shift over the course of spring to summer in the nature of limiting nutrients, from P- to N-limitation. First, the mixed flagellate-diatom assemblage assayed 5/31/2018 showed no response in the Chl signal. The conclusion that these assemblages were not nutrient limited is in agreement with the fact that these assays were performed at the time of year when lake DIN:DIP is starting to reach its minimum (Fig. 5G). Early (6/28/2018) and late (7/12/2018) summer bioassays showed clear N-limitation, but no synergistic effect of N and P additions as has been described elsewhere (reviewed in Paerl et al. 2016). At the time these assays were performed, Deal Lake DIN:DIP had been low for about one to two months (Fig. 5), due to the combined effect of DIN depletion and DIP accumulation. The continuing rainfall during this period (Jul–Oct) likely delivers high DIN loads through stormwater runoff, creating episodic opportunities for growth and perhaps, toxin production. While both N and P can potentially enter the lake water column through allochthonous and/or autochthonous (e.g. Søndergaard et al. 2013) sources, the pattern of DIP accumulation observed in the low-rainfall summer period in Deal Lake strongly suggests an autochthonous source. The apparent accumulation of autochthonous DIP drives Deal Lake toward N-limitation when cyanoHABs are present. Deal Lake is shallow (5.9 ft (1.8 m) average depth), a characteristic that favors sediment-driven nutrient cycling due to the high sediment surface to volume in shallow systems (Pace and Prairie 2005). Lake sediments can be a sink for P under aerobic and oxidizing conditions, but establishment of anaerobic or reducing conditions due to organic matter loading of the sediment surface (Moore et al. 1998), as well as elevated pH (Christophoridis and Fytianos 2006) that favors release of P to the water column. Additionally, sedimentation of cyanobacterial biomass can change lake nutrient fluxes. Chen et al. (2014) experimentally demonstrated increased P mobilization, related to elevated rates of iron and sulfur reduction, from Lake Taihou (China) sediments after amendment with cyanobacterial bloom biomass. Further, benthic feeding common carp (Cyprius carpio, Linnaeus 1758) are abundant in Deal Lake (Tiedemann et al. 2009), and a study in shallow Kohlman Lake (MN) showed a 55–92% increase in P available for release in areas where carp were active (Huser et al. 2016), suggesting another potential source of elevated P release from Deal Lake sediments. The correlation between elevated pH and HAB biomass occurring in Deal Lake likely generates conditions at the sediment surface that favors the release of sediment-bound P after lakes are loaded with DIN over the winter–spring, helping sustain cyanoHABs. Average Deal Lake water temperatures measured in this study reached 84.2 °F (29 °C) in July of 2017, and 82–84 °F (28–29 °C) in July–August of 2018. That was warmer than the average Deal Lake temperatures of 66.6–68.9 °F (19.3–20.5 °C)) reported for that time of year in a 1978 comprehensive study carried out by NJ DEP (Wagner 1978). These elevated temperatures can be expected to favor cyanobacterial dominance over competitor chlorophytes and diatoms (Paerl and Huisman 2008), particularly in the presence of excessive nutrient loading. There are two likely causes of Deal Lake warming. First, infilling of the lake by sediment runoff has Urban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 15 reduced lake depth, and therefore volume, according to long-time residents, such that solar insolation would heat the remaining water volume to a higher temperature than previously attained. Second, climate change impacts in NJ include a 38 °F (3 °C) increase in annual average temperatures and an increase in the number of days with temperatures above 95 °F (35 °C) over the last century (Runkel et al. 2017). In combination, these two factors have likely resulted in a warmer Deal Lake than existed 42 years ago (Wagner 1978), and are contributing to the ongoing cyanoHAB issues experienced there. Species Composition and Potential Toxicity The species composition of summer 2018 Deal Lake HABs can be interpreted as an indicator of N-overloading (Paerl 2018) because the two main species present, Microcystis and Pseudanabaena, are not N-fixers (Paerl and Otten 2013). This conclusion can appear contradictory, however, considering the low levels of DIN, low DIN:DIP, and bioassay results during bloom periods reported here, all of which point to N-limitation. Views on the factors favoring non- N-fixing cyanobacteria, particularly Microcystis, have evolved to include the acknowledgment that other environmental factors can support the dominance of non-N-fixing forms in N-limited environments (Paerl and Otten 2016). Species composition data available for the May–July bioassays conducted in 2018 show a succession from flagellate and diatom dominance in May to predominance of Microcystis, Pseudanabaena, and less so, Dolichospermum (which can fix N) in cyanoHAB water of Deal Lake later in the summer. This apparently non-intuitive dominance of non-N-fixers in N-limited temperate lakes has been observed elsewhere and attributed to factors other than N-availability as the driving force of cyanobacterial community composition. It includes the affinity of species like Microcystis for growth at high temperatures typical of late-season temperate lakes, as well as Microcystis’ versatility in N-form utilization including inorganic and organic forms, and the competitive disadvantage of N-fixation stemming from its energetic costs, micronutrient requirements, and oxygen sensitivity (reviewed in Paerl and Otten 2016). Later season water temperatures between 75 and 86 °F (25 and 30 °C) observed in this study are consistent with water temperature being a predominant factor in late season Microcystis abundance in Deal Lake. The low toxicity of the 2018 Deal Lake cyanobacteria bloom is likely related to the nutrient conditions, particularly low DIN, present in the lake during summer blooms. The nutrients feeding a bloom not only affect growth, but can also affect the toxicity of cells making up the cyanoHAB population because toxins such as microcystin are N-rich molecules (Gobler et al. 2016). Although speculative due to a paucity of toxin data collected during these years (Table 1), declining microcystin concentrations between 7/2/2018 and 8/27/2018 occurs over the time period of N-limitation as shown through nutrient time series (Fig. 5C) and nutrient addition bioassays (Fig. 7). There are two important corollaries of this tentative conclusion that deserve further attention. First, blooms occurring earlier in the season when N is more prevalent may be more toxic per unit biomass than late-season N-limited blooms, although low cell numbers might limit overall lake toxicity. Second, rainfall or other events occurring mid- to late-summer that introduce large DIN loads, establishing high-density cyanoHABs, may result in ephemeral increases of toxicity that could easily be missed by routine monitoring. For coastal lakes like Deal Lake that drain to the ocean at swimming beaches, the potential for exposure of bathers to high cell density and/or toxic outflows also needs to be considered. Conclusion and Management Implications Deal Lake provides a small-scale model system for examining the relationship between nutrient loading, climate, and the growth of freshwater cyanoHABs in highly urbanized enUrban Naturalist J.E. Adolf, K. Saldutti, E. Conlon, E. Ernst, B. Heddendorf, S. Shifren, and R. Schuster 2022 No. 57 16 vironments. Based on this preliminary analysis of monitoring data and nutrient addition bioassays, Deal Lake fits the profile of a lake experiencing cyanoHABs due to a combination of anthropogenic eutrophication and elevated water temperatures. Management actions should target watershed improvements aimed at decreasing seasonal nutrient loading through tributary and stormwater inputs, but should also cautiously consider dredging to remove sediment P, as Deal Lake is small enough to make this feasible, but results from other lakes are variable (e.g. Hamilton et al. 2016, Paerl 2018). New Jersey’s 2013 fertilizer law banning P and requiring at least 20% slow-release N (NJDEP 2013) will not address legacy P already in lake sediments. The dynamics described here in fact suggest that the magnitude of HABs in Deal Lake will increase with DIN loading rather than P because excess autochthonous P is available in summer. The question of whether early season blooms or summer blooms experiencing anomalously high DIN-loading through storms achieve higher toxicity needs to be addressed in a management context. Although Deal Lake is small relative to other lakes experiencing HABs nationally, it exists within a densely populated and highly developed watershed. New Jersey is in fact the most densely populated state in the US, and towns and cities along the New Jersey shore experience dramatic seasonal population increases. A Monmouth County study determined the average summer daytime population increased 73% over the average year-round population (Monmouth County Planning Board 2008), so the population increase coincides with the timing of Deal Lake cyanoHABs. These factors, combined, make the potential impacts of HABs in New Jersey coastal lakes on human populations greater than would be suggested by their size. 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