Theodore W. Lewis

Phytoplankton Composition and Biomass in the Offshore Waters of Lake Erie: Pre- and Post-Dreissena Introduction (1983–1993)

Phytoplankton was collected in all basins of Lake Erie during 42 cruises during the spring and summer from 1983 to 1993—a period that spans the Dreissena mussel invasion. Two potential impacts of Dreissena on the phytoplankton community of the western, central, and eastern basins of Lake Erie were evaluated: Was selective feeding occurring as observed in Saginaw Bay and were reductions in biomass evident in the offshore regions of the three basins of Lake Erie? In the western basin, significant summer decreases in Chlorophyta, Bacillariophyta, Cyanobacteria, and total phytoplankton biomass were observed after Dreissena introduction. Similarly in the spring, Bacillariophyta and total phytoplankton biomass and chlorophyll a concentrations decreased significantly. Since several divisions of phytoplankton did not decrease in phytoplankton biomass in the western basin, and spring Cyanobacteria biomass increased significantly while other divisions decreased in biomass, selective feeding on the phytoplankton community was suggested. Where significant reductions in biomass were observed in the offshore waters of the western basin, they were approximately 50% of the reduction observed at the nearshore sites in Lake Erie by other workers. Dreissena impact on the phytoplankton community of the pelagic waters of the central and eastern basin appeared to be minimal. Pre- and post-Dreissena total phytoplankton biomass and chlorophyll a concentrations were not significantly different or increased significantly after the Dreissena invasion. Biomass of several divisions of phytoplankton significantly increased after Dreissena introduction in the central and eastern basins. These included Bacillariophyta (central basin), Cyanobacteria (central and eastern basin), Chrysophyta (eastern basin), Chlorophyta biomass (eastern basin) and phytoplankton biomass (central basin) and chlorophyll a (central basin) in the spring, and Chrysophyta (eastern basin) and Cryptophyta biomass (central basin) in the summer. Generally, a reduction in phytoplankton biomass would be expected as a result of Dreissena grazing, not an increase in biomass. Dreissena-mediated changes in phytoplankton have generally occurred in shallow, well-mixed lakes, ponds, and embayments, not in deeper waters such as the central and eastern basins of Lake Erie.

Chemistry of the offshore surface waters of Lake Erie: pre- and post-Dreissena introduction (1983-1993).

Major changes in ambient surface nutrient chemistry were observed after the introduction of Dreissena to Lake Erie. For example, statistically significant increases in spring soluble reactive phosphorus (SRP) (180%, 1.0 to 2.8 μg P/L), nitrate+nitrite (40%, 0.57 to 0.80 mg N/L), ammonia (131%, 15.1 to 34.9 μg N/L), silica (75%, 0.8 to 1.4 mg/L), N:P ratio and turbidity and a significant decrease in total Kjeldahl nitrogen (TKN) (25%, 0.24 to 0.18 μg N/L) were observed in the western basin from the 1983 to 1987 pre-Dreissena baseline period to the 1989 to 1993 Post-Dreissena period. In the summer, total phosphorus (TP) (13%, 20.1 to 17.5 μg P/L) and TKN (27%, 0.30 to 0.22 μg N/L) decreased, while nitrate+nitrite (122%, 0.18 to 0.40 mg N/L) and the N:P ratio increased significantly. Fewer chemical parameters changed significantly in the central and eastern basins, but major changes were observed. For example, spring SRP concentrations in the central and eastern basins increased 250% (0.8 to 2.8 μg P/L) and 92% (2.4 to 4.6 μg P/L), respectively. Silica in these basins increased 300% (0.1 to 0.4 mg/L) and 250% (0.2 to 0.7 mg/L), respectively. TKN decreased in all basins in both the spring and summer (range = 22 to 27%), while TP decreased in all basins in the summer (range = 13 to 24%) but not in the spring. Spatially, spring Post-Dreissena (1989 to 1993) ammonia, TP, and nitrate+nitrite concentrations were high in the western basin and decreased easterly, while chloride concentrations were variable with no downward or upward trend. In the central basin and eastward through the eastern basin, concentrations of ammonia, chloride, nitrate+nitrite, and total phosphorus were remarkably consistent during and between the pre- and Post-Dreissena periods. After the Dreissena invasion, a different spatial pattern of SRP, silica and phytoplankton biomass was observed. SRP and silica concentrations were high in the western basin and decreased into the central basin as in the pre-Dreissena period. Similarly, Post-Dreissena SRP and silica concentrations were low in the western portion of the central basin but then unexpectedly increased easterly by > 250% and > 1,000%, respectively, over the pre-Dreissena period. Phytoplankton biomass increased from within the west end of the western basin to a peak about halfway into the central basin, after which biomass decreased into the eastern basin. The increase in the dissolved fraction of nutrients in the western basin can be attributed to the excretion of dissolved fractions by Dreissena spp. after digestion of particulate matter, the remineralization of surficial organic sediments containing nitrogen and phosphorus-rich feces and pseudofeces and to a decrease in uptake of SRP by less abundant populations of phytoplankton in the western basin. In the western portion of the central basin, it is possible that SRP is being carried by the prevailing westerly current into the central basin stimulating phytoplankton population growth combined with minimal Dreissena grazing causing a peak in phytoplankton abundance. There does not appear to be a satisfactory explanation for the simultaneous increase in SRP and the lack of any change in phytoplankton pre- and Post-Dreissena in the eastern portion of Lake Erie.

The Impact of Agricultural Best Management Practices on Downstream Systems: Soil Loss and Nutrient Chemistry and Flux to Conesus Lake, New York, USA

ABSTRACT Six small, predominantly agricultural (>70%) watersheds in the Conesus Lake catchment of New York State, USA, were selected to test the impact of Best Management Practices (BMPs) on mitigation of nonpoint nutrient sources and soil loss from farms to downstream aquatic systems. Over a 5-year period, intensive stream water monitoring and analysis of covariance provided estimates of marginal means of concentration and loading for each year weighted by covariate discharge. Significant reductions in total phosphorus, soluble reactive phosphorus, nitrate, total Kjeldahl nitrogen, and total suspended solids concentration and flux occurred by the second year and third year of implementation. At Graywood Gully, where Whole Farm Planning was practiced and a myriad of structural and cultural BMPs were introduced, we observed the greatest percent reduction (average = 55.8%) and the largest number of significant reductions in analytes (4 out of 5). Both structural and cultural BMPs were observed to have profound effects on nutrient and soil losses. Where fields were left fallow or planted in a vegetative type crop, reductions, especially in nitrate, were observed. Where structural implementation occurred, reductions in total fractions were particularly evident. Where both were applied, major reductions in nutrients and soil occurred. After 5 years of management, nonevent and event concentrations of total suspended solids in streams draining agricultural watersheds were not significantly different from those in a relatively “pristine/reference” watershed. This was not the case for nutrients.

A Decade of Predatory Control of Zooplankton Species Composition of Lake Michigan

Abstract From 1983 to 1992, 71 species representing 38 genera from the Calanoida, Cladocera, Cyclopoida, Mysidacea, Rotifera, Mollusca and Harpacticoida comprised the offshore zooplankton community of Lake Michigan. Our data demonstrate that the composition and abundance of the calanoid community after 1983 is not unlike that of 1960s and that species diversity of the calanoid community is more diverse than the cladoceran community in the 1990s as compared to the early 1980s. Even though the relative biomass of the cladocerans has remained similar over the 1983–1993 period, the species diversity and evenness of the Cladocera community in the early 1990s is unlike anything that has been previously reported for Lake Michigan. Cladocera dominance is centered in one species, Daphnia galeata mendotae, and only three species of Cladocera were observed in the pelagic region of the lake in 1991 and 1992. Nutrient levels, phytoplankton biomass, and the abundance of planktivorous alewife and bloater chub and Bythotrephes are examined as possible causes of these changes in zooplankton species composition. The increase in Rotifera biomass, but not Crustacea, was correlated with an increase in relative biomass of unicelluar algae. Food web models suggest Bythotrephes will cause Lake Michigans plankton to return to a community similar to that of the 1970s; that is Diaptomus dominated. Such a change has occurred. However, correlational analysis suggest that alewife and bloater chubs (especially juveniles) are affecting size and biomass of larger species of zooplankton as well as Bythotrephes .

Changes in Phytoplankton Size-class Abundance and Species Composition Coinciding with Changes in Water Chemistry and Zooplankton Community Structure of Lake Michigan, 1983 to 1992

Phytoplankton and zooplankton were collected at offshore sites of Lake Michigan during 37 cruises in the spring and summer from 1983 to 1992. For the period, 39 common phytoplankton species accounted for 96.0% of the total abundance and 85.6% of the biomass. Over the 10-year study, the lake-wide average spring and summer phytoplankton biomass in the pelagic waters ranged from 0.27 to 1.2 g/m3 (mean ± S.E. = 0.54 ± 0.03 g/m3) and phytoplankton abundance ranged from 5,132 to 39,780 cells/mL (mean ± S.E. = 18,291 ± 822 cells/mL). Mesotrophic diatoms accounted for 47.2% of the total phytoplankton biomass. The lack of a trend in the ratio of mesotrophic to eutrophic diatom indicator species suggested that no change in trophic status of the pelagic region occurred during the 1983 to 92 period; that is, the water quality of the offshore of Lake Michigan did not change. A year-to-year shift in dominance from one mesotrophic diatom species to another was evident. Over the 10-year period, flagellates accounted for 52.2% of the summer phytoplankton biomass. The data support the concept of a shift in summer species composition away from blue-green algae dominance to flagellates prior to 1982. However after 1987, the relative importance of the > 70 μm size class increased to over 21% of the phytoplankton abundance in the spring and over 55% in the summer. In particular, the colonial blue-greens, Anacystis and Aphanothece, became substantially more prevalent during the summer, while the flagellates, Chromulina and Ochromonas, decreased in abundance. The changes in the relative abundance of phytoplankton size classes and species composition were examined to determine if they correlated with either the top-down mediated changes in the zooplankton community during the 1980s and 1990s or with any bottom-up variability in nutrient chemistry. Canonical correspondence analysis (CCA) suggested a significant portion of the variability of the spring and summer phytoplankton size classes from 1983–1992 (88.0% and 99.2%, respectively) was explained by environmental axis 1. Primary determinants of relative abundance of phytoplankton size class included nutrients (silica, total phosphorus, and N:P ratio) and abundance of some species of zooplankton. Specifically, Diaptomus minutus, D. ashlandi, D. sicilis, and Daphnia galeata mendotae were inversely correlated with the 0 to 10 μm size class, which we interpret as a grazing effect on phytoplankton size structure, and positively correlated with an increase in abundance of the > 70 μm size class of phytoplankton. CCA suggested that top-down and bottom-up effects were affecting phytoplankton size composition and abundance simultaneously.

Management of Agricultural Practices Results in Declines of Filamentous Algae in the Lake Littoral

ABSTRACT Filamentous algal cover was quantified during periods of peak biomass from 2001 to 2007 in six littoral macrophyte beds in Conesus Lake, New York (USA). Three of the study sites were adjacent to streams that drained sub-watersheds where extensive agricultural best management practices (BMPs) designed to reduce nutrient runoff were implemented beginning in 2003. Three other study sites were downstream from sub-watersheds where only a few or no BMPs were implemented by landowners. For the sites that received extensive management, comparisons of the Pre-BMP baseline period (2–3 yrs) to the Post-BMP period (4 yrs) revealed that algal cover was statistically lower than baseline in eight of eleven years (72.7%). For the three sites where limited or no management was implemented, the percent cover of filamentous algae was lower than Pre-BMP baseline levels in only three of twelve years (25%). Where major reductions in cover of filamentous algae occurred, positive relationships existed with summer stream loading of nitrate and soluble reactive phosphorus to the nearshore. In some cases only nitrate loading was significantly correlated with percent cover, indicating that the relative importance of nitrogen and phosphorus to algal growth near streams may be determined by the characteristics and land use within each sub-watershed. Agricultural BMPs targeting nutrient and suspended solid runoff can effectively reduce filamentous algal growth locally along the lake littoral zone on a time scale of months to a few years and with moderate commitment of resources. This work offers a new perspective for management of the growing problem of littoral algal growth in the embayments and drowned river mouths of the Great Lakes.

Spatial and Temporal Distribution of the Cyanotoxin Microcystin-LR in the Lake Ontario Ecosystem: Coastal Embayments, Rivers, Nearshore and Offshore, and Upland Lakes

ABSTRACT Cyanotoxins, a group of hepatotoxins and neurotoxins produced by cyanobacteria, pose a health risk to those who use surface waters as sources for drinking water and for recreation. Little is known about the spatial and seasonal occurrence of cyanotoxins in Lake Ontario and other lakes and ponds within its watershed. Within the embayments, ponds, rivers, creeks, shoreside, and nearshore and offshore sites of Lake Ontario, microcystin-LR concentrations were low in May, increased through the summer, and reached a peak in September before decreasing in October. Considerable variability in microcystin-LR concentrations existed between and within habitat types within the Lake Ontario ecosystem. In general, the average microcystin-LR concentration was two orders of magnitude lower in embayment (mean = 0.084 µg/L), river (mean = 0.020 µg/L), and shoreside (mean = 0.052 µg/L) sites compared to upland lakes and ponds (mean = 1.136 µg/L). Concentrations in the nearshore sites (30-m depth) and offshore sites (100-m depth) were another order of magnitude lower (mean = 0.006 µg/L) than in the creek/river, bay/pond, and shoreside habitats. Only 0.3% (2 of 581) of the samples taken in Lake Ontario coastal waters exceeded the World Health Organization (WHO) Drinking Water Guideline of 1 µg microcystin/L for humans. In contrast, 20.4% (20 of 98) of the samples taken at upland lakes and ponds within the watershed of Lake Ontario exceeded WHO Guidelines. No significant relationship between nitrate and microcystin-LR concentrations was observed in Lake Ontario even though a significant positive relationship existed between phosphorus and phycocyanin and microcystin-LR concentrations. At an upland lake site (Conesus Lake) in the Ontario watershed, the development of a littoral Microcystis population was not observed despite high nutrient loading (P and N) into the nearshore zone, well-developed nearshore populations of filamentous Spirogyra and Zygnema, the occurrence of Dreissena spp., and the known occurrence of Microcystis and microcystin production in the pelagic waters of Conesus Lake.

Winter application of manure on an agricultural watershed and its impact on downstream nutrient fluxes.

ABSTRACT Whole Farm Planning was instituted and monitored over a 5-year period within the Graywood Gully sub-watershed of Conesus Lake, NY (USA). An array of agricultural Best Management Practices (BMPs) (strip cropping, fertilizer reduction, tiling, manure disposal practices, etc.) were simultaneously introduced to determine the impact of a concentrated management effort on nutrient and soil loss from one watershed within the Conesus Lake catchment. During the study period, significant decreases in winter concentrations of dissolved and particulate fractions, including total phosphorus (TP), soluble reactive phosphorus (SRP), total Kjeldahl nitrogen (TKN), and nitrate (NO3) but not total suspended solids (TSS), were observed. These decreases may or may not be attributed to cessation of manuring practices. Three years into the study, an opportunity existed to test the responsiveness of the watershed to the curtailment of a single BMP — winter manure application to fields. We field-tested the hypothesis that a change in winter manure applications would impact dissolved and particulate fractions in stream water draining this watershed. We found that the water quality of Graywood Gully is very responsive to winter manure application on environmentally sensitive portions of the sub-watershed. With the short-term resumption of manure application, TP, SRP, TKN, and NO3 concentrations rose dramatically in stream water; elevated phosphorus concentrations persisted over a 5-week period. Total suspended solids, however, were not elevated after short-term manure application. Factors that affected these results were slope of the land, application of manure over snow and during a snowfall, warm air and soil temperatures, and possibly tile drainage of snowmelt water. Managers of agricultural systems must recognize that phosphorus losses from the watershed during the nongrowing season may detrimentally affect nuisance population of algae in lakes during the summer.

Additional Link in the Food Web Does Not Biomagnify a Persistent Contaminant in Lake Ontario: The Case of Cercopagis pengoi

Cercopagis pengoi is a new and abundant non-indigenous predator species in the Lake Ontario food web. We explored the impact of this predator on the levels of a chlorinated hydrocarbon in the pelagic food web through assessments of seasonal abundance and mirex concentrations of Cercopagis pengoi (Ostroumov) and the planktivorous alewife (Alosa pseudoharengus). Abundance, stable isotope, and alewife stomach data indicate that Cercopagis pengoi has become an established portion of the Lake Ontario food web. Cercopagis, a predaceous cladoceran, feeds on the lower portion of the trophic web and is clearly fed upon by the planktivorous alewife. Cercopagis is a link in the Lake Ontario food web, in which energy and materials are being passed from one level of the trophic web to another. However, mirex levels of the planktivorous alewife did not increase during the period of highest Cercopagis abundance. The annual load of mirex (mass of Cercopagis times concentration) transferred from one level of the trophic web to the next is low. In the summer, when Cercopagis is abundant, alewives were not feeding on them.

Uptake and Retention of Mirex By Fish Maintained on Formulated and Natural Diets in Lake Ontario Waters

Abstract Fish with no detectable levels of the contaminant mirex were grown in Lake Ontario waters under conditions simulating commercial aquaculture. Benthic black bullheads (Ameiurus melas) were grown in cages placed in a bay of the lake. Pelagic rainbow trout (Oncorhynchus mykiss) were grown in terrestrial raceways served with Lake Ontario waters. Contaminant-free fingerlings were reared to a large size on a commercial ration in these systems, which partially isolated them from the contaminant-laden food web and bottom sediments. Black bullheads fed a mirex-spiked, commercially prepared food had mirex concentrations that exceeded the U.S. Food and Drug Administration (FDA) action level of 0.1 μg/g, significantly higher than concentrations in fish receiving the same commercial food without mirex. Ninety percent of fish receiving the unspiked ration had nondetectable levels of mirex (values below 0.002 μg/g). The 10% containing mirex had concentrations 94% below FDA action level. In the rainbow trout stu...