Harmful Algae Bloom Occurrence in Urban Ponds: Relationship of Toxin Levels with Cell Density and Species Composition
2Department of
Biological Sciences, Northern Kentucky University, Highland Heights, KY, USA
Citation: Cruz ADL, Logsdon R, Lye D, Guglielmi S, Rice A, et al. (2017) Harmful Algae Bloom Occurrence in Urban Ponds: Relationship of Toxin Levels with Cell Density and Species Composition. J Earth Environ Sci: JEES-148. DOI: 10.29011/2577-0640.100048
1. Abstract
Retention ponds constructed within urban watershed areas of high density populations are common as a result of green infrastructure applications. Several urban ponds in the Northern Kentucky area were monitored for algal community (Algae and Cyanobacteria) from October 2012 to September 2013. Many of the harmful algal blooms observed during this study were composed primarily of the cyanobacteria genus, Microcystis. No correlations were observed between basic water quality parameters (dissolved oxygen, pH, conductivity, temperature, nitrate and soluble reactive phosphate) and the presence of cyanobacteria and/or microcystin cyanobacterial toxin levels. Furthermore, levels of microcystin toxins did not always coincide with high Microcystis cell counts. Harmful algal blooms in small urban ponds are common which pose risk to human and ecological health due to proximity of dense human population including pets and wild animals. Because harmful algal blooms were detected throughout the year in this study, adaptation of universal guidelines for the design, construction and maintenance of urban ponds may be necessary to protect watershed aquatic ecosystems, and lower health risks from exposure to such harmful blooms.
Keywords:Cyanobacteria;Harmful Algal Bloom; Microcystin; Microcystis;Urban ponds
1. Introduction
Urbanization can be a major contributor to the eutrophication of aquatic ecosystems within a watershed area. Agricultural runoff, wastewater discharge, and storm water runoff often carry excess nutrients into the urban watershed and create conditions in which algae and cyanobacteria (both will be referred to as “Algae”) will thrive [1-3]. Urban ponds containing high levels of algae can lead to “Nuisance blooms” which can produce foul odors, disrupt the scenery and develop into harmful blooms containing dangerous toxin (Harmful Algal Blooms, HABs).
HABs readily occur in shallow, warm, eutrophic waters and have been reported world-wide [4]. In the Ohio/Kentucky region, HABs have been commonly reported in the Great Lakes, Grand Lake St. Mary’s (in Ohio) and the Ohio River [5-7]. Although aquatic ecosystems, which are important tourist attractions and/or drinking water sources, receive the most attention, many individuals may also come into almost daily contact with small ponds in their immediate neighborhoods. There is a need for documentation of the occurrence and types of harmful algal and cyanobacterial blooms in small pond ecosystems commonly found in urban watersheds.
Artificial ponds constructed within areas of high density populations are commonplace. A majority of consumers in an urban watershed would pay more for property located in a neighborhood with stormwater control structures designed to enhance fish and wildlife use (NAICHI.org). Although many metropolitan areas incorporate local urban stormwater ponds in accordance with Green Infrastructure (GI) applications (which are beneficial in flood control) these same GI sites may pose environmental and human health risks due to biological and chemical contamination, and as breeding grounds for insects and other animals[8].
In one of the few studies concerning small pond ecosystems within an urban watershed, Lewitus et al.[9] reported the occurrence of HABs in a study of 1,500 ponds located along the South Carolina (USA) coast. Their study suggested that the incorporation of residential and golf course retention ponds is a common management practice intended to reduce impacts of pollutants (sewage, fertilizer, pesticides, herbicides, etc.) on the urban watershed, but these same local aquatic ecosystems may also inadvertently create an ideal environment for HABs. In another study of 3,500 Dutch eutrophic urban ponds, highly toxic cyanobacterial blooms were reported with microcystin toxin levels as high as 64,000 ppb in scums, and 77 ppb in water [10]. Previous studies have also associated harmful blooms being “triggered” by relatively high temperatures, alkaline pH and nutrient enrichment [11].
Additional studies are needed to determine the extent of exposure to harmful toxins from HABs occurring right in the backyards of residents within an urban watershed. Illnesses caused by exposure to cyanobacteria are difficult to diagnose, and therefore the number of reported cases may be lower than what actually occurs [1,12]. Acute exposure may cause gastrointestinal problems, dermatitis, liver failure, and even death, but chronic exposures could possibly lead to conditions such as asthma, allergic sensitivities, neurological distress, kidney damage or liver tumors [3,13-15].
Abiotic data are often insufficient for predicting the variability often found within cyanobacterial blooms. Biotic factors such as the presence of heterotrophic bacterioplankton and protists are emerging as being highly influential to the make-up of the phytoplanktonic communities giving rise to blooms [16]. It remains difficult to predict the onset, duration and intensity of blooms in both large and small freshwater ecosystems due to the lack of knowledge concerning the processes leading to the dominance of any one cyanobacterial species. There is also a paucity of studies which document all of the cyanobacterial participants before, during and after bloom events which occur in small freshwater ponds [17].
In this study, we report both the occurrence of algal blooms and the percentage of all cyanobacteria genera present in individual algal blooms monitored in five small ponds constructed in urban developments and recreational areas in the Northern Kentucky area. Correlations of water quality parameters with the presence of cyanobacteria and total microcystin toxin levels were also examined. Microcystis aeruginosa was found to dominate the communities in the ponds during the study. Microcystis can successfully compete against other photosynthetic organisms because of its ability to migrate to different depths within the water column [18]. Microcystis is also capable of survival at higher pH and conductivity levels [12] commonly found in waters of the Northern Kentucky area (due to the high mineral concentrations.
2. Results
During the 32 sampling events reported in this study, 24 (75%) of the samples met World Health Organization (WHO) guidelines for recreational water harmful bloom (cyanobacterial counts ≥ 20,000 cells mL-1) [19]. See (Tables 1 and 2) for a characterization of the 32 sampling events and sites. (Figure 1) shows the sampling sites. For comparison purposes, the sampling events are listed according to the level of microcystin toxin detected and not based on location. Twenty-one (21) of the 32 sampling events (66%) met WHO guidelines for recreational water HABs (microcystin level ≥ 4 ppb) (Table 1).
Twenty-five (25) of the 32 sampling events (78%) were dominated by Microcystis spp. (at least 90% of total cells present were Microcystis spp.). Of the 25 samples dominated by Microcystis spp., 18 occurred with levels of microcystin detected at > 4 ppb (72% would be classified by WHO as HABs, 28% would not be classified as HABs).
Sample #21 (Glen Arbor Upper) contained only 34% and 10.7% Microcystis and Anabaena spp., respectively, but did show a level of > 4 ppb microcystin which would meet the WHO guidelines to be classified as a HAB.
The algae communities found in sampling events #24, #26 and #30 had Microcystis spp. levels at 21%, 54% and 41%, respectively. Despite the presence of Microcystis, all of these samples yielded very low levels of microcystin concentrations.
Two sampling events yielded no (zero) Microcystis spp. (#4 listed in Table 1, and #28 listed in Table 2). Very low level of micro cyst in toxin (0.4 ppb) was detected in sample #28 although the cyanobacteria Planktothrix sp. was also detected in this sample and could have produced toxin. In contrast, sample #4 collected on June 2013 (Valeside Pond) was described as “a scummy and dark green colored water”.Pandorina/Volvox were readily observed and dominated in this sample (no Microcystis spp. were seen microscopically) with 577.67 ppb microcystin toxin level.
Fifteen (15) of the 21 HABs (71%) monitored in the study also met the “High Probability of Acute Health Effects” according to WHO recreational water guidelines due to the microcystin concentrations > 20 ppb. However, during this study there were no samples containing Microcystis spp. counts higher than 100,000 cells mL-1, and there was no noticeable evidence of fish or animal deaths in the sampling areas.
The concentrations of microcystins in samples taken from the urban ponds in this survey varied day to day and month to month. Although 13 of 21 (62%) sampling events yielding HAB levels of microcystin toxin (> 10 ppb) were documented in the three summer months of June, July and August, there were no readily discernable patterns exhibited by the microcystin concentrations over time and seasons (Tables 1 and 2).
HABs were detected year-round in multiple ponds with the most toxic bloom occurring at Loch Norse in January 2013 (1,286 ppb microcystin) when the water temperature was at 3.3°C. HABs were also detected at Redbud in October 2012 and at Loch Norse on March 2013 during cooler temperatures (Figure 2).
In this
study, there were no significant correlations found between the levels of
microcystin toxin and either conductivity (R2 =
0.0436, Figure 3), or temperature (R2 =
0.0000153, Figure 4). No significant correlations were also noted with Microcystis spp.
with nitrate (r2=0.001) and soluble phosphate (r2=0.0043).
3. Discussion
The WHO recreational water guidelines [19]for algal blooms do not address the types of species involved in the blooms, and not all algal blooms are toxic. In harmful algal blooms, a mixture of toxic and non-toxic species of cyanobacteria can occur [20]. Documentation of the type(s) of species occurring within a bloom may therefore be necessary to properly inform citizens about the possibility of toxins being present. Taxonomic classification of cyanobacteria is currently undergoing changes. Microscopic identification of the composition of a bloom can be erroneous. WHO states that counts greater than 20,000 cells mL-1 are necessary to classify a bloom as low health risk [21]. However, three samples (#s 10, 14 and 21) containing < 20,000 cells mL-1 had microcystin levels and general condition of the pond suggesting a HAB. An example of this was seen in the results reported for sampling event #4 (obvious bloom, no Microcystis spp. observed microscopically, high levels of microcystin detected). One possibility could be that Microcystis cells may have been present previous to the sampling time but had either lysed or migrated away by the time of the sampling. It is also possible that other microcystin-producing genera or species may have been present. Results such as these would suggest that the WHO recreational water guidelines should be expanded to include the monitoring of toxins other than microcystin.
The results of our study suggest that algal blooms are quite common in small ponds constructed in urban development’s and recreational areas. Seventy-five percent of the sampling events exhibited cyanobacterial cell counts greater than the WHO recreational water guidelines. These blooms were detected throughout the year (even in adverse cold conditions, usually not associated with harmful cyanobacterial blooms). Sixty-six percent of the blooms also exhibited high levels (> 4 ppb) of microcystin toxin).
Because some of the HABs occurred in our study of small urban ponds during periods of cold weather, it is possible that urban HABs could pose a year-round hazard (not just in the warmer summer months). Microcystis is known to produce higher concentrations of toxin at lower temperatures in the laboratory [22], but to our knowledge this has not been studied in an environmental setting. Cells of Microcystis spp. dominated the blooms observed during the study. However, high microcystin levels were also found in the absence of Microcystis dominance.
Unlike larger bodies of water, our results did not establish a correlation between microcystin toxin levels and other water quality parameters measured in this study. There were no significant correlations between toxicity and either pH or dissolved O2% (data not shown). The natural levels of nitrate in water is < 1 mg L-1. Nitrate levels in these pondsranged from 0.6 - 70 mg L-1(mean = 2.094, median = 1.2, mode = 1.03) and is not a limiting factor in the growth of cyanobacteria on these ponds. Toxic blooms of M. aeruginosa had been reported in nitrogen-limited conditions [23-27].Soluble reactive phosphate level in these ponds are low (range = 0 - 3.0 µg L-1, mean = 0.21, median 0.20; data not shown) and showed no correlationwith Microcystis spp. cell count and total microcystin level (r2 = 0.0043 and 0.0285, respectively; data not shown).
Despite efforts to control phosphate in aquatic environments, harmful blooms still occur [28]. In this study, soluble phosphate was not associated with the number of cells and microcystin levels.Microcystisspp. can reabsorb phosphate and store polyphosphate granules as reserve [29]. Previous studies reported contradictory effects of phosphate with Microcystis growth and toxin production [30-32]. Water quality parameters including nutrients may not be associated with Microcystis spp. and microcystin toxins in small artificial urban ponds since the hydrogeologic conditions (physical-chemical parameters) and biotic conditions are different compared with bigger bodies of water like lakes and rivers. Small urban ponds may not follow the same ecological patterns as larger natural bodies of water[33,34].
The
small artificial ponds in our study, unlike lakes and rivers where blooms
appear mostly in the summer, do not have much sediment build-up to act as
nutrient sinks. The ponds where heavy blooms occurred in our study also
contained little to no buffer zones whereas the ponds that had lily pads,
trees, grasses and animal life had less severe harmful bloom events. This is
most likely due to the plants’ effective removal of nutrients from the water.
4. Materials and Methods
4.1. Study Sites
Sies were selected by availability to the public, proximity to homes, or suggested by concerned residents. A pond was defined as having surface area less than five acres, or 20,234 m2[9]. The study sites are shown in (Figure 1) and briefly described below.
Loch Norse (39o01’52.64’N, 84o27’46.65’W)
Loch Norse is a renovated farm pond in Highland Heights, KY, USA, located in the center of the campus of Northern Kentucky University (NKU). The pond is shallow and aerated by an artificial waterfall. The pond is divided into two sections, with the northern perimeter surrounded by concrete, and the southern perimeter surrounded by cattails, bulrushes and water iris. The pond contains goldfish, and both ducks and geese nest in the surroundings. Loch Norse has been monitored for many years by one of us (MSK) and has recurrent algal blooms. NKU grounds-keeping staff treats the water with copper sulfate and “AquaShade®” pond dye twice a year.
Redbud Pond (39o01’52.64’N, 84o27’46.65’W)
Redbud Pond is a man-made retention pond located in a residential subdivision. Residents routinely report blooms that create foul odors and unsightly conditions in the summer, along the perimeter of the pond and in the residents’ back yards. The perimeter is lined with grasses, cattails and bulrushes. The pond is aerated by three pumps. Grass carp and bluegill are seen frequently in the shallows. There are “no fishing” signs along the shore of the pond.
Glen Arbor Ponds (upper; 39o00’17.58’’N, 84o40’06.08’’W)
These are two ponds located in a local public golf course. The northernmost pond was designated as “Glen Arbor Upper Pond,” while the southern pond was designated “Glen Arbor Lower Pond”. Golfers routinely reported algae blooms producing foul odors in the Glen Arbor Upper Pond in July 2013. Sampling occurred regularly, with verbal permission from the golf course manager. Other than manicured turf, no plants surround the ponds. The ponds are not aerated, but are connected by a small waterfall.
Valeside Pond (38o58’35.09’N 84o31’22.81’W) and Crystal “Lake” (38o58’59.40’’N, 84o31’24.50”W)
These are small retention ponds located in the same residential subdivision. Valeside Pond is surrounded by trees, cattails and various grasses. It slopes off quickly near the shore. Crystal “Lake” is at the entrance of the subdivision. There is very little turf and no other plants surrounding the pond. The ponds are not aerated and the backyards of several homes are aligned along their perimeter.
4.2. Monitoring and Plankton Collection
For this study, ponds were sampled from a designated area for each site regardless of whether a bloom was observed or not (Table 1). From October 2012 to September 2013, dissolved oxygen (DO), pH, conductivity, temperature and nitrate were monitored using a YSI Multiparameter Water Quality Instrument (Profession Plus model; Yellow Springs, OH, USA). Phosphate level was also determine using Hach Total Phosphate Kit according to the manufacturer (Hach Company, Loveland, CO, USA). Whole water samples were collected just below the surface using a Van Dorn horizontal 2.2 L water sampler. Approximately 1.0 L of the sample was stored in amber glass bottles and transported back to the lab in a cooler for processing.
4.3. Cell Counts
Unpreserved whole water samples were immediately examined with a compound microscope for total algae diversity and dominant species. Some Microcystislyse when preserved, so this immediate “Qualitative count” was necessary to assure accuracy when Microcystiswas present. Lugol’s iodine was then added to whole water samples then the samples were allowed to settle overnight. Cell counts were performed using an inverted microscope based on the EPA’s Standard Operating Procedure (SOP) for Phytoplankton Analysis [36].
4.4. Total Microcystin Analysis
Two mL whole water samples were frozen at -20oC freezer, gently thawed in a warm water bath for 1-2 minutes, and frozen at -20°C again. This process was repeated twice in order to fully lyse the cells. The samples were then tested for the presence of total microcystin toxins (extracellular and intracellular), using the Envirologix™ ELISA kit (Envirologix QuantiPlate™for Microcystins, Portland, ME, USA). The kit negative control was analyzed in six replicates and standards and test samples in triplicate. Per cent coefficient of variation were < 15%. To quantitate microcystins in a test sample, dilutions were prepared (2-3 dilutions) and analyzed in triplicate. Diluted test samples were within the standard curve linear range. If the optical density (with corresponding microcystin concentration) was below or above the linear range, sample dilution was readjusted and reanalyzed. Samples tested negative were reported as below detection limit. The Molecular Devices SpectraMax M2 spectrophotometer with Software Pro version 4.8 (Molecular Devices Corporation, Sunnyvale, CA, USA) was used to record the absorbance, calculated the mean, % CV, r2 and generated graphs for the standard calibrators.
4.5. Determining if an Algal Bloom was a HAB
Although the US EPA has not established guidelines as to what level of cell counts constitute a bloom, the Agency does define a bloom as the “visible coloration of a water body due to the presence of suspended cells, filaments and/or colonies and, in some cases, subsequent surface scums[37]. The World Health Organization’s guidelines are based upon both cyanobacterial cell numbers/mL and toxin levels (WHO 2003). Cell density ≥ 20,000 cells/mL is classified as harmful bloom (low risk), and if the microcystin concentration is ≥ 4 ng/mL (ppb), the bloom is considered a HAB[38,39].
4.6. Ethics Statement
No
specific permissions were required for the activities performed at the
locations chosen for this study because they are all publicly accessible sites.
No field study involved endangered or protected species.
Figure 1: Study
sites in Northern Kentucky with their corresponding GPS location (source:
google maps). Water samples were collected on October 2012 to September 2013.
Figure 2:
Total microcystin level trends at five study sites from October 2012 to
September 2013. There was no distinct pattern noted at the five different
ponds.
Figure 3:
The relationship of total microcystin level and water conductivity. No
correlation was noted between microcystin toxin levels and water conductivity.
Figure 4:
Relationship of microcystin toxin levels and temperature. The total microcystin
levels showed no correlation with the water temperatures.
Srl. No. |
Site
|
Sampling Date |
Total Microcystin |
Microcystis sp. Cell Count |
%Composition of Speciesb |
(ppb) |
(cells mL-1) |
||||
1 |
Loch Norse |
01-09-13 |
1286 |
29,301 |
97.3% Microcystis sp. |
2 |
Loch Norse |
10/25/2012 |
851 |
28,701 |
97.8% Microcystissp. |
3 |
Redbud |
6/24/2013 |
724 |
57,402 |
99.4% Microcystissp. |
4 |
Valeside |
6/18/2013 |
577.67 |
0 |
0.0 % Microcystis sp. |
5 |
|
|
|
|
50.0% Pandorina sp. |
6 |
|
|
|
|
50.0% Pandorina sp. |
7 |
Redbud |
06-05-13 |
552.55 |
30805 |
98.2% Microcystis sp. |
8 |
Glen Arbor U |
08-02-13 |
423.29 |
86103 |
99.3% Microcystissp. |
9 |
Redbud |
6/26/2013 |
404.78 |
28641 |
97.8% Microcystis sp. |
10 |
Redbud |
07-10-13 |
340.68 |
28642 |
94.8% Microcystis sp. |
11 |
Glen Arbor U |
6/26/2013 |
195.15 |
26631 |
98.2% Microcystissp. |
12 |
Loch Norse |
3/20/2013 |
74.79 |
13362 |
91.6% Microcystis sp. |
13 |
Loch Norse |
1/30/2013 |
59.26 |
29001 |
86.2% Microcystissp. |
14 |
Redbud |
10-11-12 |
57.19 |
28701 |
95.7% Microcystissp. |
15 |
Loch Norse |
4/30/2013 |
51.33 |
29001 |
98.9% Microcystissp. |
16 |
Glen Arbor U |
07-10-13 |
48.75 |
13130 |
98.1% Microcystis sp. |
17 |
Redbud |
7/26/2013 |
28.11 |
28701 |
98.3% Microcystis sp. |
18 |
Redbud |
08-02-13 |
15.81 |
86103 |
99.3% Microcystis sp. |
19 |
Glen Arbor L |
08-02-13 |
15.28 |
29,001 |
97.0% Microcystis sp. |
20 |
Loch Norse |
5/21/2013 |
13.84 |
57402 |
100.0% Microcystissp. |
21 |
Loch Norse |
05-07-13 |
11.81 |
57402 |
100.0% Microcystis sp. |
22 |
Loch Norse |
06-05-13 |
10.31 |
28701 |
98.6% Microcystis sp. |
23 |
Glen Arbor U |
7/25/2013 |
10.03 |
382 |
34.3% Microcystissp. |
|
|
|
|
|
50.0% Euglena sp. |
|
|
|
|
|
10.7% Anabaenasp. |
|
|
|
|
|
4.6% Aulacoseira sp. |
a≥ 4 ppb microcystin [19], blooms listed according to microcystin concentration bBlooms usually dominated by Microcystisspp., minor components of community not listed unless comprising more than 4.0 % of community. |
Table 1: Urban pond algal blooms in the Northern Kentucky area with high micro cysteine concentrationsa(HABs).
Srl.No.
|
Site |
Date |
Total Microcystin |
Microcystis spp. Cell Count |
%Composition of Speciesb |
|
|
|
(ppb) |
(cells mL-1) |
|
1 |
Glen Arbor L |
7/25/2013 |
3.75 |
28704 |
97.2% Microcystissp. |
2 |
Loch Norse |
41339 |
2.17 |
28701 |
98.6% Microcystissp. |
3
|
Crystal
|
6/18/2013
|
1.76
|
478
|
21.3% Microcystissp. 13.3% Fragillaria sp. 13.3% Cryptomonas sp. 4.0 % Ankistrodesmussp. 48.1% Other |
|
|||||
4 |
Redbud |
1/28/2013 |
1.25 |
57115 |
98.6% Microcystissp. |
5
|
Valeside
|
5/29/2013
|
1.25
|
470
|
53.7% Microcystissp. 13.8% Cyclotella sp. |
13.2% Aulacoseirasp. 19.3% Other |
|||||
6 |
Redbud |
11/15/2012 |
0.98 |
86103 |
98.5% Microcystis sp. |
7
|
Crystal
|
7/25/2013
|
0.4
|
0
|
0.0% Microcystissp. 26.9% Cyclotella sp. 15.3%Oocystis sp. 12.1% Planktothrix sp. |
45.7% Other |
|||||
8 |
Loch Norse |
3/18/2013 |
0.15 |
25387 |
94.0% Microcystissp. |
9
|
Crystal
|
5/29/2013
|
0.02
|
300
|
40.6% Microcystis sp. 14.3% Cyclotellasp. 14.2% Ankistrodesmussp. |
30.9% Other |
|||||
10 |
Loch Norse |
41278 |
0.01 |
28701 |
95.5% Microcystissp. |
11 |
Loch Norse |
41222 |
0 |
28701 |
98.1% Microcystissp. |
a ≤ 4 ppb MC-LR [20], blooms listed according to microcystin concentration b Blooms usually dominated by Microcystisspp., minor components of community not listed unless comprising more than 4.0 % of community |
Table 2: Urban pond algal blooms in Northern Kentucky area with low microcystinconcentrationsa.
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