Saginaw Bay Research Articles

Q&A: Interview with David Fielder

FisheriesVolume 40, Issue 4 p. 150-151 Interview Q&A: Interview with David Fielder Returning to Graduate School as a Professional – Perspectives from a Non-Traditional Student Jeff Schaeffer, Jeff Schaeffer AFS Co-Chief Science Editor jschaeffer@usgs.gov David Fielder is a research biologist for the Michigan Department of Natural Resources stationed in Alpena, Michigan, on Lake Huron. During 2014, Fielder had many professional accomplishments and was a co-recipient of the American Fisheries Society President's Fishery Conservation Award for his work on conservation and management of the Saginaw Bay fish community. But his greatest achievement last year was receiving a Ph.D. from the Michigan State University Department of Fisheries and Wildlife. Fielder had been working professionally for many years before deciding to seek that degree, and we interviewed him to learn about his experience and gain insight into how he did it so that other fisheries professionals might take advantage of his knowledge to further their own educational goals.Search for more papers by this author Jeff Schaeffer, Jeff Schaeffer AFS Co-Chief Science Editor jschaeffer@usgs.gov David Fielder is a research biologist for the Michigan Department of Natural Resources stationed in Alpena, Michigan, on Lake Huron. During 2014, Fielder had many professional accomplishments and was a co-recipient of the American Fisheries Society President's Fishery Conservation Award for his work on conservation and management of the Saginaw Bay fish community. But his greatest achievement last year was receiving a Ph.D. from the Michigan State University Department of Fisheries and Wildlife. Fielder had been working professionally for many years before deciding to seek that degree, and we interviewed him to learn about his experience and gain insight into how he did it so that other fisheries professionals might take advantage of his knowledge to further their own educational goals.Search for more papers by this author First published: 15 April 2015 https://doi.org/10.1080/03632415.2015.1027160 Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume40, Issue4April 2015Pages 150-151 RelatedInformation

High resolution spatially explicit nutrient source models for the Lower Peninsula of Michigan

Nutrient loading to aquatic systems has been linked to many issues including eutrophication, harmful algal blooms, and decreases in species diversity. In the Great Lakes, algal blooms continue to plague Lake Erie and Saginaw Bay despite reductions in point source loading. Here, methods for predicting nutrient sources using GIS are described to examine the link between watershed nutrient sources, landscape processes, and in-stream loads in the Lower Peninsula of Michigan. These models predict all significant nutrient sources to the landscape at 30 m resolution over a 144,000 km2 region, avoiding the tradeoff between scale and source detail common to many existing watershed nutrient models. The model results presented here indicate that there is a high degree of variability in nutrient landscape loading rates, even within the same land use class. Within all land use types, except unmanaged lands, loading rates for most major sources varied by at least an order of magnitude. This work provides valuable information that can be used by environmental managers regarding how and where to target efforts to reduce nutrient loads in surface water particularly in the Great Lakes region where management efforts have been ongoing since the 1960s.

Benthic algal response to invasive mussels in Saginaw Bay: a comparison of historical and recent data

Benthic algal communities in the Laurentian Great Lakes (USA and Canada) have been strongly affected by the invasion of dreissenid mussels. Early (1990–1995) studies in Saginaw Bay, Lake Huron, demonstrated a shift from light to nutrient (phosphorus, P) limitation of benthic algae, and large changes in benthic algal community composition once zebra mussels (Dreissena polymorpha) became established. We conducted benthic algal sampling and a nutrient enrichment experiment at a historic sampling site to quantify benthic algae under current environmental conditions and to compare current results with historical data. Benthic algal P-demand was apparently saturated immediately post-invasion, but in subsequent years, algal growth on artificial substrata was consistently P-limited (p always <0.005), perhaps as a result of declining mussel abundance. Epilithic benthic algal community composition displayed large interannual changes, perhaps in response to mussel-induced alteration of light availability and natural changes in substratum characteristics at this site.

Acoustic telemetry reveals large-scale migration patterns of walleye in Lake Huron.

Fish migration in large freshwater lacustrine systems such as the Laurentian Great Lakes is not well understood. The walleye (Sander vitreus) is an economically and ecologically important native fish species throughout the Great Lakes. In Lake Huron walleye has recently undergone a population expansion as a result of recovery of the primary stock, stemming from changing food web dynamics. During 2011 and 2012, we used acoustic telemetry to document the timing and spatial scale of walleye migration in Lake Huron and Saginaw Bay. Spawning walleye (n = 199) collected from a tributary of Saginaw Bay were implanted with acoustic tags and their migrations were documented using acoustic receivers (n = 140) deployed throughout U.S. nearshore waters of Lake Huron. Three migration pathways were described using multistate mark-recapture models. Models were evaluated using the Akaike Information Criterion. Fish sex did not influence migratory behavior but did affect migration rate and walleye were detected on all acoustic receiver lines. Most (95%) tagged fish migrated downstream from the riverine tagging and release location to Saginaw Bay, and 37% of these fish emigrated from Saginaw Bay into Lake Huron. Remarkably, 8% of walleye that emigrated from Saginaw Bay were detected at the acoustic receiver line located farthest from the release location more than 350 km away. Most (64%) walleye returned to the Saginaw River in 2012, presumably for spawning. Our findings reveal that fish from this stock use virtually the entirety of U.S. nearshore waters of Lake Huron.

Methodology and determination of tetradecabromo-1,4-diphenoxybenzene flame retardant and breakdown by-products in sediments from the Laurentian Great Lakes

Tetradecabromo-1,4-diphenoxybenzene (TeDB-DiPhOBz) is a brominated polyphenyl ether flame retardant (FR) that is known to photolytically degrade to produce lower brominated polybrominated-diphenoxybenzenes (PB-DiPhOBzs), which may be precursors to MeO-PB-DiPhOBzs recently reported in the Great Lakes herring gulls eggs. To our knowledge, there are no reports on TeDB-DiPhOBz or other PB-DiPhOBz by-products in any environmental sample. The present study analyzed for the presence of PB-DiPhOBzs (including TeDB-DiPhOBz) and MeO-PB-DiPhOBzs in surficial sediment from sites in Saginaw Bay in western Lake Huron (n=7), and in comparison to southern Lake Huron (open water) (n=5) and Lake Erie (n=3) sediment collected in the summers of 2012 or 2013. To analyze for possible PB-DiPhOBzs (Br14–Br0), the first known analytical method was developed for extraction and cleanup of sediment samples, and analysis by HPLC–atmospheric pressure photoionization (−)-quadrupole time-of-flight-mass spectrometry. The overall recovery efficiency was optimized to on average 33–104% progressing from Br14- to Br10-PB-DiPhOBzs. Br10- to Br14-PB-DiPhOBz detection and quantification limits ranged from 0.05 to 0.15ngg−1 dw and 0.17 to 0.49ngg−1 dw, respectively. Although this is the first report, PB-DiPhOBzs (Br14–Br10) and MeO-PB-DiPhOBzs were not detectable in any sediment sample. This included a site near the mouth of the highly FR-contaminated Saginaw River, near the confined disposal facility (CDF) located in Saginaw Bay at Channel-Shelter Island, which receives dredged sediment from the Saginaw River. Our findings suggest sediments from the presently studied sites in the Great Lakes ecosystem are not a sink for TeDB-DiPhOBz and PB-DiPhOBz by-product contaminants.

Changes in the Saginaw Bay, Lake Huron, fish community from 1970–2011

Many aquatic ecosystems experience concurrent anthropogenic stressors that can have complex impacts on fish communities. Limited data and temporal associations among environmental stressors may confound the ability to attribute community-level impacts to single or multiple stressors. Instead, quantitative description of temporal changes in fish communities may shed light on the cumulative and individual impacts of diverse stressors. Saginaw Bay, Lake Huron, has experienced diverse anthropogenic stressors that have been inconsistently quantified over time. We used resampling and multivariate approaches to analyze long-term trawl data to describe how fish community patterns changed in Saginaw Bay from 1970–2011. Total, native, and moderately tolerant fish species richness generally increased from 1970–2011. Dynamic factor analysis and nonmetric multidimensional scaling revealed that fish community structure changed from 1970–2011 and that relative abundances of many fish species increased. In general, increases in richness and CPUE were correlated with decreases in total phosphorus, chl a, and water levels. In addition, breakpoint analyses revealed shifts in species richness in the mid-1980s and 1999. Temporal patterns are consistent with the hypothesis that the Saginaw Bay fish community has changed from one dominated by species tolerant of eutrophy to one with more sensitive species, likely a response to decreased phosphorous loading and resulting changes in water quality. More recently (1999–2011), richness and relative abundance of many fish species in Saginaw Bay declined, a pattern potentially reflective of larger food-web transitions in both Saginaw Bay and open Lake Huron.

Integration of Auxiliary Information in Statistical Catch‐at‐Age (SCA) Analysis of the Saginaw Bay Stock of Walleye in Lake Huron

AbstractEstimates of mortality rates and abundance for the Saginaw Bay stock of Walleye Sander vitreus has traditionally been performed with an analysis of tag returns using a Brownie‐style analysis. An estimation approach that more fully accounted for sources of exploitation in addition to the recreational fishery in Saginaw Bay and inclusive of the rest of Lake Huron was needed. We developed a statistical catch‐at‐age model to accomplish this and evaluated four versions including three different treatments of natural mortality (M): a constant value, age‐based M values, and time‐varying M values. Deviance information criterion model selection procedures indicated that an age‐based M model version was optimal. We also evaluated an integrated version that incorporated tag returns as auxiliary information for the recreational component. In this case, model selection was based on conformity between observed and predicted data and model convergence. The integrated version was ruled out due to poor agreement of the observed and predicted values and predictions of abundance that were not reflected by the fisheries. We concluded that the component of the population used for tagging may exhibit dynamics that differ from the rest of the stock. Total annual mortality of Walleyes was greatest for older ages in all fisheries and ranged from 32% for age‐2 fish to 39% for fish of ages 10 and older. The recreational fishery accounted for the majority of fishing mortality, but the commercial trap‐net fishery in the main basin of Lake Huron and bykill from other trap nets in the bay accounted for proportionally greater fishing mortality of younger ages of fish. Abundance peaked in 2007 at 4 million Walleyes age2 and older, but estimates indicated a previous period of high abundance in the late 1980s, forcing the reconsideration of the past stock as depressed and dependent on stocking.Received January 8, 2014; accepted June 11, 2014

Quantifying storage changes in regional Great Lakes watersheds using a coupled subsurface‐land surface process model and GRACE, MODIS products

AbstractAs a direct measure of watershed resilience, watershed storage is important for understanding climate change impacts on water resources. In this paper we quantify water budget components and storage changes for two of the largest watersheds in the State of Michigan, USA (the Grand River and the Saginaw Bay watersheds) using remotely sensed data and a process‐based hydrologic model (PAWS) that includes detailed representations of subsurface and land surface processes. Model performance is evaluated using ground‐based observations (streamflows, groundwater heads, soil moisture, and soil temperature) as well as satellite‐based estimates of evapotranspiration (Moderate‐resolution Imaging Spectroradiometer, MODIS) and watershed storage changes (Gravity Recovery and Climate Experiment, GRACE). We use the model to compute annual‐average fluxes due to evapotranspiration, surface runoff, recharge and groundwater contribution to streams and analyze the impacts of land use and land cover (LULC) and soil types on annual hydrologic budgets using correlation analysis. Watershed storage changes based on GRACE data and model results showed similar patterns. Storage was dominated by subsurface components and showed an increasing trend over the past decade. This work provides new estimates of water budgets and storage changes in Great Lakes watersheds and the results are expected to aid in the analysis and interpretation of the current trend of declining lake levels, in understanding projected future impacts of climate change as well as in identifying appropriate climate adaptation strategies.

Large watershed management and restoration: dioxin sediment remediation case study

This paper reviews continuing, long-term remediation of river sediments containing dioxin and other chemical compounds in a large watershed of the Great Lakes Region. Chlorinated dibenzo-p-dioxins are a ‘family’ of chemically related compounds commonly known as chlorinated dioxins or simply, dioxins. The highest levels are usually found in sediments, soil and animal fats. The most toxic chemical in this group is 2,3,7,8-tetrachlorodibenzo-para-dioxin, the ‘standard’ to which other dioxins are compared and which has been shown to be very toxic in animal studies. The US Environmental Protection Agency (EPA) and Michigan Department of Environmental Quality (MDEQ) have made a lengthy effort to assess and remediate portions of the Saginaw Bay Watershed, including the Tittabawassee River. The paper reviews the EPA-proposed ‘phased approach’ to restoration and remediation of a short segment (Segment 1) of the Tittabawassee River sediments. Sediments are contaminated with a number of chemical pollutants other than dioxins, including arsenic, cholorbenzenes, cholorphenols, ethyl parathion, o-phenylphenol and polycyclic aromatic hydrocarbons. The paper evaluates three proposed ‘cleanup alternatives’, with final action method suggested based on effectiveness, feasibility for implementation and cost.

Summer circulation and exchange in the Saginaw Bay-Lake Huron system

We use a three-dimensional, unstructured grid hydrodynamic model to examine circulation and exchange in the Saginaw Bay-Lake Huron system during the summer months for three consecutive years (2009–2011). The model was tested against ADCP observations of currents, data from a Lagrangian drifter experiment in the Saginaw Bay, and temperature data from the National Data Buoy Center stations. Mean circulation was predominantly cyclonic in the main basin of Lake Huron with current speeds in the surface layer being highest in August. Circulation in the Saginaw Bay was characterized by the presence of an anticyclonic gyre at the mouth of the outer bay and two recirculating cells within the inner bay. New estimates are provided for the mean flushing times (computed as the volume of the bay divided by the rate of inflow) and residence times (computed as e-folding flushing times based on dye concentration modeling treating the bay as a continuously stirred tank reactor) for Saginaw Bay. The average flushing time (over the 3 months of summer and for all 3 years) was 23.0 days for the inner bay and 9.9 days for the entire bay. The mean e-folding flushing time was 62 days (2 months) for the inner bay and 115 days (3.7 months) for the entire bay for the summer conditions examined in this work. To characterize the behavior of river plumes in the inner Saginaw Bay, trajectory data from GPS-enabled Lagrangian drifters were used to compute the absolute diffusivity values in the alongshore and cross-shore directions.

A Bayesian network incorporating observation error to predict phosphorus and chlorophyll a in Saginaw Bay

Empirical relationships between lake chlorophyll a and total phosphorus concentrations are widely used to develop predictive models. These models are often estimated using sample averages as implicit surrogates for unknown lake-wide means, a practice than can result in biased parameter estimation and inaccurate predictive uncertainty. We develop a Bayesian network model based on empirical chlorophyll-phosphorus relationships for Saginaw Bay, an embayment on Lake Huron. The model treats the means as unknown parameters, and includes structure to accommodate the observation error associated with estimating those means. Compared with results from an analogous simple model using sample averages, the observation error model has a lower predictive uncertainty and predicts lower chlorophyll and phosphorus concentrations under contemporary lake conditions. These models will be useful to guide pending decision-making pursuant to the 2012 Great Lakes Water Quality Agreement.

Influence of water-level fluctuation duration and magnitude on sediment–water nutrient exchange in coastal wetlands

This study examined the influence of water-level fluctuation (WLF) on sediment–water nutrient exchange in the Laurentian Great Lakes. Water levels in the Laurentian Great Lakes have been below the long-term mean for the past 15 years, causing the exposure of sediments that previously have been either continuously inundated or periodically exposed. The magnitude, duration, and frequency of WLF, as well as land-use history, each can influence the amount and type of sediment–water nutrient exchange. We collected sediment cores from relatively pristine coastal wetlands located on Beaver and Garden Islands in northern Lake Michigan. Sediment cores were taken from different water depths to simulate WLF magnitude; desiccation time was experimentally manipulated to simulate WLF duration. At these relatively pristine wetlands, desiccation time and water depth significantly influenced flux. However, nutrient exchange did not behave in a consistent fashion; phosphorus, nitrate, ammonium, and sulfate flux varied based on sediment exposure history and desiccation time. Sediment–water nutrient exchange rates also were compared to prior measurements taken from more impacted coastal wetlands in southern Lake Michigan and Saginaw Bay in Lake Huron. This comparison revealed a stronger influence of anthropogenic stress than desiccation time, with impacted wetland sediments releasing more soluble reactive phosphorus, sulfate, and ammonium, and retaining more nitrate, than pristine wetlands. Our results indicate that WLFs have the potential to influence sediment–water nutrient exchange, which may influence system productivity, but environmental context can override this influence.

A 200 year chronology of burrowing mayflies (Hexagenia spp.) in Saginaw Bay

After an absence of 50years, burrowing mayflies (Hexagenia spp.) colonized western Lake Erie which led to interest in whether this fauna can be used to measure recovery in nearshore waters throughout the Great Lakes. However, in many areas we do not know if mayflies were native/endemic and thus, whether recovery is a logical measure to assess progress of recovery. In the present study, we construct a chronologic record of relative abundance of burrowing mayflies in Saginaw Bay by the use of mayfly tusks and radionuclides in sediments (i.e., a paleoecologic record) and historic records of mayfly nymphs in the bay. These records reveal that mayflies: (1) were few before 1799, which indicates that nymphs were probably native/endemic in the bay, (2) increased between 1799 and 1807 and remained at relatively high levels between 1807 and 1965, probably in response to increased nutrient run-off from the watershed, (3) declined dramatically between 1965 and 1973, probably as a result of excessive eutrophication in the mid-1950s; and, (4) were few and highly variable between 1973 and 2001, probably as a result of low and unstable abundances of mayfly nymphs. Historic records verify that nymphs disappeared in the bay in the late-1950s to early-1960s which is in agreement with the paleoecologic record. Reoccurrence of low abundances of nymphs in the bay between 1991 and 2008 and comparison of chronologic records of nymphs in Saginaw Bay and western Lake Erie suggest that mayflies may return to Saginaw Bay in the early-21st century. Undoubtedly, watershed conservation and three decades of pollution abatement have set the stage for a recovery of burrowing mayflies in Saginaw Bay, and possibly in other areas of the Great Lakes.

Trends in the distribution and abundance of Hexagenia spp. in Saginaw Bay, Lake Huron, 1954–2012: Moving towards recovery?

Since at least the 1940s, multiple anthropogenic disturbances to the Laurentian Great Lakes have had detrimental effects on benthic habitats and biota including decimating the environmentally sensitive burrowing mayfly genus Hexagenia around the mid-1950s. While remediation efforts have facilitated recovery of some populations, benthic surveys in Saginaw Bay, Lake Huron in the last 50years have only occasionally discovered Hexagenia nymphs. Recently, adult Hexagenia swarms have been reported near the bay; therefore, we corroborated the local presence of Hexagenia adults and evaluated the current status of Saginaw Bay Hexagenia nymphs. We quantified adults during mayfly emergence events in 2010 at three Tawas City, Michigan, USA area locations, and found >17 Hexagenia/m2/site. We quantified nymphs from Ponar grab samples collected at 57 sites in Saginaw Bay between 2009 and 2012, and found 1.5 nymphs/m2 overall with nymphs present at 15.8% of sites sampled, their greatest documented distribution in Saginaw Bay since 1956. Additionally, we mapped bay sediment composition and related sampling site abiotic conditions with both Hexagenia presence and abundance using Zero-Inflated Poisson regression. Model results indicate that the probability of observed Hexagenia absence being true absence is positively related to both sediment sandiness and surficial dissolved oxygen concentration while Hexagenia abundance is greatest where surficial temperatures are ~18.6°C and is also related to sediment sand content. The documentation of nearby adults and in bay nymphs may indicate the beginning of a Hexagenia return to Saginaw Bay, and, therefore, a possible improvement of the ecosystem's benthic health.

Condition and diet of yellow perch in Saginaw Bay, Lake Huron (1970–2011)

In Saginaw Bay, Lake Huron, yellow perch (Perca flavescens) constitute an ecologically important component of the ecosystem and support both recreational and commercial fisheries. Over the past 40years, Saginaw Bay has experienced multiple ecosystem-level changes (e.g., non-indigenous species introductions, reduced nutrient loading and variable temperatures). In turn, abundances and growth rates of yellow perch and their predators and prey have fluctuated. Recent changes to Saginaw Bay and Lake Huron foodwebs have potential to influence prey composition and subsequently, growth and condition for yellow perch; but a complete description of yellow perch diet composition across seasons has not been undertaken in recent years. We calculated mean relative weight (Wr), an index of condition, of age-1 and older yellow perch in Saginaw Bay annually for 1970–2011. We found high interannual variation in condition and documented low mean Wr during 1978–1991. We developed regression models to explain this variation using phosphorus load, temperature, forage fish density, and yellow perch density as potential explanatory factors. Patterns of Wr were associated with changes in yellow perch densities, although interannual variation was not significantly associated with any of the available explanatory variables. Diet analysis of yellow perch collected in 2009 and 2010 demonstrated that age-1 and older yellow perch consumed a fundamentally different diet from a previous study (1986–1988), exhibiting a greater reliance on non-indigenous prey (e.g. Bythotrephes longimanus).

Patterns of age-0 yellow perch growth, diets, and mortality in Saginaw Bay, Lake Huron

Identifying mechanisms influencing early-life survival may elucidate recruitment variability of fish populations. Yellow perch (Perca flavescens), are economically and ecologically important in Saginaw Bay, Lake Huron, but have recently experienced low recruitment despite strong production of age-0 fish. Recent year classes have been characterized by slow first-year growth, as indexed by fall size of age-0 yellow perch; however, seasonal growth patterns and accompanying diet and survivorship patterns have not been documented for age-0 yellow perch in Saginaw Bay. To this end, we collected age-0 yellow perch weekly (larvae) and monthly (juveniles) throughout the first year of life during 2009 and 2010 to track changes in growth and diet composition. We also evaluated predation and over-winter energy-loss as potential mechanisms of size-selective mortality. Yellow perch growth, energy accumulation and size-specific condition decreased during late summer and fall. During larval and juvenile stages, predominant components of yellow perch diets transitioned from copepods to Daphnia and other zooplankton; however, we observed only weak ontogenetic shifts toward benthic prey. Smaller yellow perch a) were preferentially preyed upon by walleye (the bay's main piscivore) and b) displayed lower mass-specific energy content, potentially increasing overwinter starvation risk, suggesting that slow growth increases mortality risk. Our results are consistent with the hypothesis that recruitment dynamics are influenced by an interplay of size-selective mortality and diet-induced reductions in growth.

Spatial and temporal patterns of macroscopic benthic primary producers in Saginaw Bay, Lake Huron

We investigated spatial and temporal patterns in macroscopic benthic primary producer biomass, production, and composition in inner Saginaw Bay in 2009 and 2010. Charophytes and filamentous algae (FA) were relatively abundant, and vascular macrophytes were less common. The probability of benthic primary producer presence increased with the proportion of benthic substrate composed of rock. Most benthic primary producer biomass occurred at depths of 2–4m, with very little biomass observed beyond 4m deep. Charophyte and vascular macrophyte abundances displayed consistent patterns related to distance from the mouth of the Saginaw River. FA abundance also displayed such patterns, but they reversed between 2009 and 2010. Macrophytic benthic primary producer communities were generally dominated by charophytes. Three genera of vascular macrophytes, including Myriophyllum, were also observed. Filamentous algal communities were composed of a mixture of FA taxa. Ten FA genera were observed, including the red alga Compsopogon. Dominance of Compsopogon was related to low water clarity and low TP. Biomass-based benthic production estimates indicated that charophytes and FA strongly dominated macroscopic benthic production; production of vascular macrophytes was relatively low. The observed relationships of abundance and environmental conditions suggested regulation of benthic producer biomass by a shifting mosaic of substratum, nutrient, and light availabilities. The diverse nature of the benthic producer community could complicate understanding and management of excess benthic biomass and beach fouling in Saginaw Bay.

A reflection on restoration progress in the Saginaw Bay watershed

The Saginaw Bay watershed is unique and remains one of the most diverse watersheds in Michigan, containing the largest contiguous freshwater coastal wetland system in the United States. The watershed and Saginaw Bay support a wide variety of flora and fauna, agriculture and recreation opportunities. However, the rapid industrialization and population growth of the watershed in the 20th century strained the region's natural resources. Excessive nutrient loading, elevated bacteria levels, aquatic habitat loss, and chemical contamination all altered the watershed's ecosystem. These stressors contributed to declining fish and wildlife populations, loss of coastal wetlands, water quality concerns, beach closings, and the buildup of contaminants in the food web. Over the past four decades, extensive federal, state, and regional priority-based assessments and planning have positioned the Saginaw Bay watershed for significant restoration. There is a continued commitment by federal, state, and regional partners to advance restoration efforts. This paper reflects upon those activities and provides additional actions that would aid restoration work in the Saginaw Bay watershed and in the Saginaw Bay, a region of the Great Lakes that still must address significant environmental challenges to reach its full potential.

Microzooplankton distribution, dynamics, and trophic interactions relative to phytoplankton and quagga mussels in Saginaw Bay, Lake Huron

Invasive quagga mussels have recently replaced zebra mussels as the dominant filter-feeding bivalves in the Great Lakes. This study examined microzooplankton (i.e., grazers <200μm) and their trophic interactions with phytoplankton, bacteria, and bivalve mussels in Saginaw Bay, Lake Huron, following the zebra to quagga mussel shift. Microzooplankton distribution displayed strong spatial and temporal variability (1.73–28.5μg C/L) relative to phytoplankton distribution. Ciliates were the dominant component, especially in the spring and early summer. Rotifers and dinoflagellates increased toward late summer/fall in the inner and outer parts of the bay, respectively. Microzooplankton grazing matched bacterial growth rates and removed ca. 30% of the phytoplankton standing stock in the <100μm size fraction per day. The greatest herbivory occurred at the site dominated by colonial cyanobacteria. Microzooplankton, which comprised <4% of the quagga mussels prey field (i.e. available prey), contributed 77% and 34% to the quagga carbon-based diet during Microcystis and diatom blooms, respectively. Feeding on microzooplankton could buffer mussels during lean periods, or supplement other consumed resources, particularly during noxious cyanobacterial blooms. The results of this study demonstrate that microzooplankton are a resilient and critical component of the Saginaw Bay ecosystem.

Estimating point and non-point source nutrient loads in the Saginaw Bay watersheds

Databases of point sources including combined sewer overflows (CSOs) were acquired from the governmental agencies to map the occurrences and magnitude of the CSOs. Multiple databases of land use, topography, hydrography, soils, and agricultural statistics were used to estimate nonpoint source loading potential in the Saginaw Bay Basin, Michigan. Animal manure production was computed from tabulations of animals by 5-digit zip code area for the census years of 1987, 1992, 1997, and 2002. Fertilizer applications for both urban and agricultural land uses were calculated from county fertilizer estimates for the same periods. Results indicate that point sources from municipalities, industrial sectors and business entities contribute approximately 25% of the total phosphorus load to Saginaw Bay, with the remainder being accounted for by nonpoint source contributions. While the total amount of nutrients (N and P) from animal manure and fertilizer applications and atmospheric deposition declined in the Saginaw Bay Basin, fertilizer applications in non-farmland increased significantly. Estimation of nutrient loading potential at 5-digit zip code level reveals more detailed spatial variation and critical areas of nutrient loading than county level data for implementation of targeted water quality programs.