Southeastern Lake Michigan Research Articles

Factors affecting rotifer assemblages along a nearshore to offshore transect in southeastern Lake Michigan

Rotifer assemblages have been widely used as indicators of trophic conditions. Our goal was to evaluate whether differences in rotifer assemblages along a nearshore to offshore transect in southeastern Lake Michigan were consistent with productivity differences among sites. Sampling took place in March-December during 2013–2019 at a nearshore (17-m deep), mid-depth (45-m deep), and offshore site (110-m deep). Conochilus and Keratella were present in most samples (84–100%) and were the most abundant taxa overall at each site, combining for around 64–69% by density of the rotifers. Although the productivity gradient was not large between sites, there was a progression with the highest contributions of Keratella, Conochilus, and Kellicottia occurring at the nearshore, mid-depth, and offshore sites, respectively, which is consistent with a gradient of decreasing productivity from nearshore to offshore. The rotifer community also demonstrated strong seasonal patterns. In particular, there was a progression from dominance by illoricate forms, particularly Synchaeta, early in the season, to loricate and colonial forms in the summer and fall. Redundancy analysis indicated that in addition to productivity (i.e., total phosphorus), predatory factors (e.g., cyclopoid copepods, Cercopagis, Bythotrephes) had a strong influence on the rotifer community and seasonal patterns. Although productivity was important in structuring rotifer assemblages along our nearshore to offshore gradient, other factors, especially those related to predation, are difficult to separate from productivity effects. This complexity somewhat limits the usefulness of rotifers as an indicator group for productivity among sites that do not have extreme differences in trophy within a lake.

Variable changes in zooplankton phenology associated with the disappearance of the spring phytoplankton bloom in Lake Michigan

Abstract Changes in seasonal cycles (i.e., phenology), can cause mismatches throughout aquatic food webs and often are used as the primary indicator of zooplankton response to environmental changes. However, zooplankton phenology has been largely overlooked in Lake Michigan despite the altered phenology of phytoplankton, including the disappearance of the offshore spring phytoplankton bloom following Dreissena mussel invasions. Multiple measures of phenology were evaluated for the major zooplankton groups in offshore southeastern Lake Michigan both before the loss of the spring bloom (1983–2003), and after the spring bloom had disappeared (2007–2019). Water temperatures in spring did not differ between time periods. Standardised biomass declined between time periods for all zooplankton groups in spring and for total zooplankton and the cladoceran Daphnia in the summer. Changes in zooplankton phenology varied across groups and depended on the phenological measures used. Month of peak biomass shifted later for all groups, but the central point of the growing season did not change for any group between time periods. The onset of population development was delayed only for the copepod Limnocalanus. Spring chlorophyll concentrations combined with spring water temperatures provided the best predictions of population onset for Limnocalanus and Daphnia. The central point of the growing season varied with spring chlorophyll concentrations for Limnocalanus, but with spring water temperature for Daphnia. Changes in zooplankton phenology were relatively subtle compared to the large changes observed for spring chlorophyll concentrations. By contrast, there were fairly consistent declines in zooplankton biomass across groups that were associated with the declines in spring chlorophyll either alone or in combination with spring water temperature. This may mean that food limitation has a stronger influence on zooplankton biomass or production than on zooplankton phenology in offshore Lake Michigan. Based on our results from Lake Michigan, alterations such as nutrient reduction or invasive dreissenid mussel filtering that lead to declines in spring phytoplankton blooms in other large freshwater lakes could result in subtle delays in zooplankton phenology for some groups along with stronger declines in zooplankton biomass.

Seasonal patterns for Secchi depth, chlorophyll a, total phosphorus, and nutrient limitation differ between nearshore and offshore in Lake Michigan

Data on Secchi depth, chlorophyll a, total phosphorus (TP), and nutrient status of phytoplankton were collected at five nearshore sites (11–17 m deep) and two offshore sites (>100 m) between the Grand River and Muskegon River outflows during March-December 2014–2018 to describe seasonal patterns and to compare the two depth regions in southeastern Lake Michigan. In contrast to the offshore, where spring chlorophyll a and TP concentrations declined dramatically following the dreissenid mussel expansion, the nearshore region of southeastern Lake Michigan was still characterized by low Secchi depth and elevated chlorophyll a and TP in the spring. During May, median Secchi depth was 5 times higher in the offshore than the nearshore, whereas chlorophyll a and TP were over 9 and 3 times higher in the nearshore, respectively. Even though spring chlorophyll a and TP have declined substantially at some of the nearshore sites compared to 1996, particularly the sites closest to tributary outflows, the overall yield of chlorophyll a per unit TP did not change over time in the nearshore. There were indications of P-deficiency in the nearshore in 2014–2018, but P-deficiency was even more severe in the offshore during the spring where yield of chlorophyll a per unit TP was also lower than in the nearshore. Although dreissenid mussels can be abundant in the nearshore, their populations are patchy and inputs from tributaries provide conditions that apparently dampen any potential filtering impacts of mussels in the nearshore compared to the offshore, especially during the spring.

The influence of ontogeny and prey abundance on feeding ecology of age‐0 Lake Whitefish (Coregonus clupeaformis) in southeastern Lake Michigan

AbstractA shift towards oligotrophic conditions in Lake Michigan has led to concern that altered trophic pathways are leading to lower early life survival and recruitment for Lake Whitefish (Coregonus clupeaformis). This study evaluated ontogenetic shifts in age‐0 Lake Whitefish diets and evaluated how feeding ecology and the amount of food eaten varied with prey abundance and composition at a site in southeastern Lake Michigan during 2014–2017. Although prey densities varied among years, cyclopoid copepods were overall the most abundant prey available. In turn, cyclopoids were the predominant prey item in diets each year, particularly for the smallest larval Lake Whitefish. However, there was a tendency for the importance of cyclopoids to decline somewhat in each diet index as fish grew and other prey such as calanoid copepods, Bosminidae, Daphniidae and/or chironomids increased in importance. High zooplankton abundance, especially high cyclopoid abundance, available to the small size groups of Lake Whitefish (<21 mm) in 2014 was associated with high food mass/fish, high number of zooplankton eaten/fish, and low incidence of empty stomachs compared with 2015–2017. As fish grew, the impact of food abundance on prey consumption diminished somewhat, indicating that the relationship between fish feeding ecology and the prey environment can change quickly with fish size during the early life period.

Seasonal feeding ecology of co-existing native and invasive benthic fish along a nearshore to offshore gradient in Lake Michigan

Relative abundance, diet composition and feeding strategy were determined for three benthic fish, the native deepwater sculpin Myoxocephalus thompsonii (Girard, 1851) and slimy sculpin Cottus cognatus (Richardson, 1836), and the invasive round goby Neogobius melanostomus (Pallas, 1814), along a nearshore to offshore gradient in southeastern Lake Michigan during March–December 2010, 2015, and 2016. Round goby were most abundant in the nearshore ( 75 m). Despite a large degree of spatial separation, some species did overlap, with slimy and deepwater sculpin occurring in sympatry throughout the year in the offshore and transitional zones, and round goby overlapping with both sculpin species seasonally in the transitional zone. Deepwater sculpin exhibited specialization on Mysis diluviana in all depth regions. Slimy sculpin in the offshore reduced diet overlap with deepwater sculpin by specializing on fish eggs during spring and fall, whereas in the transitional depth zone, there was considerable overlap between sculpin species due to the high importance of Mysis in diets. The invasive round goby had a mixed diet, with some diet overlap with native sculpin, especially slimy sculpin, in the transitional zone. In the nearshore zone, round goby displayed a generalized diet with many prey contributing to the diet, but the average contribution of any prey was generally low. Spatial separation and variable feeding strategies help reduce, but not eliminate shared resource use amongst these benthic fish in Lake Michigan.

Changes in water quality variables at a mid-depth site after proliferation of dreissenid mussels in southeastern Lake Michigan

Changes in water quality variables at a mid-depth site after proliferation of dreissenid mussels in southeastern Lake Michigan

Zooplankton trophic structure in Lake Michigan as revealed by stable carbon and nitrogen isotopes

Abstract Within the last few decades Lake Michigan's plankton community has undergone substantial changes. Oligotrophication of the pelagic zone has led to a decrease in zooplankton biomass, while species composition has shifted, with copepod species becoming more dominant. Although these observations have been relatively well documented, their implications for the food web have not been well addressed. To define feeding relationships within the zooplankton community, we measured the stable carbon and nitrogen isotope composition and biomass of major zooplankton species, three seston size classes, and seston collected from three depths in southeastern Lake Michigan. Nitrogen stable isotope ratios suggest a complex plankton food web with zooplankton appearing to occupy at least three distinct trophic positions. The large calanoid copepod Limnocalanus macrurus occupied a tertiary consumer trophic position, more than one trophic position above all other zooplankton species sampled. Carbon stable isotopes revealed significant differences among zooplankton species. Though the mechanisms responsible for these differences are not clear, these results suggest that there is significant partitioning of resources at the base of the food web.

Diets and growth potential of early stage larval yellow perch and alewife in a nearshore region of southeastern Lake Michigan

Abstract Transition from endogenous to exogenous feeding is thought to be a critical period for many fish larvae, when prey availability (type, size, and density) and ambient physical conditions (e.g., temperature, water clarity) can strongly influence survival. In Lake Michigan, two important fish species, yellow perch (Perca flavescens) and alewife (Alosa pseudoharengus), hatch and, presumably, begin exogenously feeding in the nearshore zone, an area characterized by short-term variation in environmental conditions. During 2010-2011, we examined environmental conditions and spatial and temporal distributions of larval yellow perch, larval alewife, and their potential prey in a nearshore region of southeastern Lake Michigan. To consider implications of environmental conditions on larval fish habitat quality, we quantified diet contents of young larval yellow perch and alewife and modeled bioenergetic growth rate potential (an index of habitat quality) under observed and predicted prey consumption scenarios. As expected, in this dynamic nearshore zone temperatures, light levels, zooplankton prey availability, and resulting growth rate potential were highly variable. Many larval fish digestive tracts were empty, suggesting that starvation may affect cohort survival. Among early-feeding larval fish, relatively small diet items were common, with larval alewives consuming diatoms and larval yellow perch consuming veligers of invasive dreissenid mussels. Though the mechanisms underlying such prey consumption and the consequences of ingesting these prey items remain largely unexplored, our results suggest dreissenid mussel veligers present early-feeding larvae with a relatively abundant prey source that may partially offset the apparent low consumption of other prey sources within Lake Michigan’s nearshore region.

Spatial and temporal trends in zooplankton assemblages along a nearshore to offshore transect in southeastern Lake Michigan from 2007 to 2012

Abstract Zooplankton were collected at a nearshore (15 m depth), a mid-depth (45 m) and an offshore site (110 m) near Muskegon, Michigan during March–December in 2007–2012. On a volumetric basis, biomass was lower at the nearshore site relative to the mid-depth site, but overall biomass at the nearshore and offshore sites did not differ. Differences in zooplankton assemblages among sites were due largely to Diaptomidae, Limnocalanus macrurus , Daphnia galeata mendotae , Cyclops , and either Bosmina longirostris or Bythotrephes longimanus . Diaptomidae were the most abundant group, accounting for 56–66% of zooplankton biomass across sites. Herbivorous cladocerans accounted for 14–22% of zooplankton biomass across sites, with B. longirostris dominant at the nearshore site and D. g. mendotae dominant at the mid-depth and offshore sites. Bythotrephes was the most abundant predatory cladoceran at all sites although, at the nearshore site, it was only abundant in the fall. There was a higher percentage of large-bodied zooplankton groups in the offshore and mid-depth zones relative to the nearshore zone. Declines in zooplankton biomass relative to the 1970s have occurred across all sites. In addition to seasonal variation within a site, we noted annual variation, especially at the offshore site, with the zooplankton assemblage during 2007–2008 differing from that found in 2010–2012 due to increases in D. g. mendotae and Cyclops and decreases in B. longimanus and L. macrurus in 2010–2012.

Lake Michigan sediment lead storage and history of loads

Dated sediment box cores collected in 1994–1996 from 52 locations in Lake Michigan were analyzed to assess storage, trends, and loading history of lead. The results of this study provide information of historic lead loads to the lake for a time period (pre-1960) for which no reliable lead measurements exist. The information can be utilized by those wishing to model lead and to access lead loading trends. Anthropogenic lead storage in the lake's sediments totaled 143,000t as of 1994. Storage of acid-extractable total (anthropogenic+background) lead totaled 171,000t between 1850 and 1994. The date of 1850 is the time at which lead loads increased above background loads (219t/y) to the lake. Anthropogenic loads peaked between 1959 and 1962 at 2440t/y and were 1170t/y between 1994 and 1995, illustrating that at the time of collection in 1994, loads were decreasing from previous highs. The load in 1994 to 1995 was equivalent to the load during the time frame of 1922 to 1925. Largest lead loads were to southeastern Lake Michigan in a region downwind of Chicago, illustrating the impact of large populated areas utilizing coal and gasoline on lead loads to the lake. Loading trends were impacted by coal and gasoline consumption, increased industrial activity during World War II, the Clean Air Act of 1970, and the phase-out of leaded gasoline.

Recent change in summer chlorophyll a dynamics of southeastern Lake Michigan

Six offshore stations in southeastern Lake Michigan were sampled during a pre quagga mussel Dreissena rostriformis bugensis period (1995–2000) and a post quagga mussel period (2007–2011). Chlorophyll a fluorescence profiles were used to characterize chlorophyll a concentrations during early (June–July) and late (August–September) summer stratification. During the early summer period the average whole water column chlorophyll a, the deep chlorophyll maximum, and the size of deep chlorophyll layer decreased 50%, 55%, and 92%, respectively, between 1995–2000 and 2007–2011. By contrast, in late summer there were no changes in these metrics between periods. Surface mixed layer chlorophyll a in early and late summer did not differ between time periods. On the other hand, chlorophyll a in the near bottom zone (bottom 20m) declined 63% and 54% between 1995–2000 and 2007–2011 in early and late summer respectively. Changes in total phosphorus between 1995–2000 and 2007–2011 were less dramatic, with declines of 22–27% in early summer and 11–30% in late summer. Changes in the chlorophyll a conditions were attributed to dreissenid mussels which reduced material available from the spring bloom and disrupted the horizontal transport of nutrients to the offshore. Although light availability increased (i.e., increased secchi depths), reduced nutrient availability and spring diatom abundance resulted in a much smaller deep chlorophyll layer in 2007–2011.

Lipid content of Mysis diluviana in the offshore region of southeastern Lake Michigan in 2009–2010

The lipid content of Mysis diluviana in the offshore region of southeastern Lake Michigan was determined in 2009 and 2010. Total lipids (mg) increased with Mysis length, but percent lipids (% dry weight) did not. Increases in lipids for juveniles (<10mm) were related to increases in structural lipids (i.e., phospholipids and sterols), whereas increases in total lipids for adults were related to increases in storage lipids (i.e., triacylglycerols). Percent lipids varied seasonally, and were in general, highest in spring or late fall for juveniles and small adults (<15mm). For the largest adults (16+mm), % lipid content did not vary much over the year in 2009, but in 2010, % lipids peaked in July. The rate of lipid retention differed among cohorts of juveniles, but it did not differ among cohorts of adults. In 2009 and 2010 respectively, 14% and 40% of Mysis >13mm had lipid content <14%, a value associated with a high percentage of docosahexaenoic acid that may reflect starvation for this size of Mysis. Food availability (chl a levels or zooplankton biomass) was not correlated with Mysis lipid content for any size group of Mysis. Seasonal gradients in food availability might not be large enough to elicit strong responses in lipid content of Mysis.

Temporal trends in Mysis relicta abundance, production, and life-history characteristics in southeastern Lake Michigan

The density and life history characteristics of Mysis relicta were evaluated at a 110-m and 45-m station in southeast Lake Michigan during spring, summer, and fall for two time periods, 1995–2002 and 2007–2008. Mysis were more abundant during 1995–2002 than 2007–2008 for all seasons and depths, with average declines across seasons of 81% at 45 m and 70% at 110 m. Offshore densities of Mysis in 2007–2008 were similar to published densities within the same region during 1985–1989, but under differing ecosystem conditions (e.g. higher fish biomass and primary production in the 1980 s). Growth averaged 0.032 ± 0.002 mm/day in both 1995–2002 and 2007–2008, and the proportion of females with broods (overall 7%) did not differ between time periods. Mean brood size adjusted for length did not differ between 1995–2002 (17 ± 0.6) and 2007–2008 (15 ± 1.3). The mean length of reproductive females was higher in 2007–2008 (17 ± 0.2) than during 1995–2002 (16 ± 0.1). New recruits (≤ 4 mm) were collected during each season for each time period, but were lower in abundance in 2007–2008 than in 1995–2002. During spring, there was a significant relationship between offshore water column chlorophyll concentration and Mysis recruit abundance, but not during summer/fall. Declining spring chlorophyll levels may be altering food availability for small mysids in spring, and the decline of the benthic macroinvertebrate Diporeia may be increasing fish predation pressure on Mysis despite declining planktivore abundance.

Recent changes in primary production and phytoplankton in the offshore region of southeastern Lake Michigan

Phytoplankton abundance, composition, and productivity were monitored on a bi-weekly basis from March/April through November/December at two offshore stations in southeastern Lake Michigan in 1983–1987, 1995–1998 and 2007–2008 (exception 1983–1984 which were sampled from May to August). During the spring isothermal mixing period, surface-mixed layer (SML) chlorophyll a and phytoplankton biomass (carbon) and water column primary productivity decreased substantially in 2007–2008 as compared to 1995–1998 (66%, 87%, and 70% decrease, respectively). Smaller or no decreases were noted between 1983–1987 and 1995–1998 (chlorophyll a 23% decrease, phytoplankton biomass 5% increase, and production 22% decrease). Phytoplankton composition also changed during the spring isothermal mixing period in 2007–2008 as compared to 1983–1987 and 1995–1998; all phytoplankton groups with the exception of cyanobacteria and chlorophytes exhibited dramatic reductions in 2007–2008. The pronounced changes in phytoplankton properties during spring mixing in 2007–2008 were attributed to the filtering activities of the quagga mussel ( Dreissena rostriformis bugensis). During mid- and late thermal stratification periods, SML phytoplankton chlorophyll a and phytoplankton carbon and water column primary production exhibited only one significant change across all decades (mid-stratification production in 2007–2008 as compared to 1995–1998 and 1983–1987). Phytoplankton compositional changes in the SML also were limited during thermal stratification. The size of the deep chlorophyll layer (DCL) in 2007–2008 was similar to or smaller than those in 1983–1987 and 1995–1998. However, phytoplankton composition in the DCL changed as net diatoms constituted < 5% of total phytoplankton in the 2007–2008 DCL but over 50% in 1983–1987 and 1995–1998.

Temporal and spatial separation allow coexistence of predatory cladocerans: Leptodora kindtii, Bythotrephes longimanus and Cercopagis pengoi, in southeastern Lake Michigan

The predatory cladocerans, Leptodora kindtii, Bythotrephes longimanus, and Cercopagis pengoi coexist in the waters of southeastern Lake Michigan near Muskegon, Michigan. Leptodora is indigenous, whereas Bythotrephes and Cercopagis are nonindigenous and became established in 1986 and 2000, respectively. To observe seasonal changes in their abundances, and relationships to each other, cladocerans were collected from 1994 to 2008 at an offshore (110-m) site, from 1998 to 2008 at a transitional (45-m) site and from 1999 to 2008 at a nearshore (15-m) site. Bythotrephes was most abundant at the offshore site compared to Leptodora and Cercopagis. Bythotrephes peak abundances usually occurred in autumn at all sites. Cercopagis tended to be more abundant at the nearshore site, and peak densities occurred in summer. At the mid-depth site, similar abundances occurred for all three predatory cladocerans, however, the date of peak abundance was usually earliest for Cercopagis, followed by Leptodora, and latest for Bythotrephes. In recent years, 2007 and 2008, densities of all three predatory cladocerans have increased. Temperature preference, fish predation, and competition between the invertebrate predators may all be important in allowing the dominance of one species over the other seasonally or spatially.

Adaptations in a hierarchical food web of southeastern Lake Michigan

Two issues in ecological network theory are: (1) how to construct an ecological network model and (2) how do entire networks (as opposed to individual species) adapt to changing conditions? We present a novel method for constructing an ecological network model for the food web of southeastern Lake Michigan (USA) and we identify changes in key system properties that are large relative to their uncertainty as this ecological network adapts from one time point to a second time point in response to multiple perturbations. To construct our food web for southeastern Lake Michigan, we followed the list of seven recommendations outlined in Cohen et al. [Cohen, J.E., et al., 1993. Improving food webs. Ecology 74, 252–258] for improving food webs. We explored two inter-related extensions of hierarchical system theory with our food web; the first one was that subsystems react to perturbations independently in the short-term and the second one was that a system's properties change at a slower rate than its subsystems’ properties. We used Shannon's equations to provide quantitative versions of the basic food web properties: number of prey, number of predators, number of feeding links, and connectance (or density). We then compared these properties between the two time-periods by developing distributions of each property for each time period that took uncertainty about the property into account. We compared these distributions, and concluded that non-overlapping distributions indicated changes in these properties that were large relative to their uncertainty. Two subsystems were identified within our food web system structure ( p < 0.001). One subsystem had more non-overlapping distributions in food web properties between Time 1 and Time 2 than the other subsystem. The overall system had all overlapping distributions in food web properties between Time 1 and Time 2. These results supported both extensions of hierarchical systems theory. Interestingly, the subsystem with more non-overlapping distributions in food web properties was the subsystem that contained primarily benthic taxa, contrary to expectations that the identified major perturbations (lower phosphorous inputs and invasive species) would more greatly affect the subsystem containing primarily pelagic taxa. Future food-web research should employ rigorous statistical analysis and incorporate uncertainty in food web properties for a better understanding of how ecological networks adapt.

Geomorphic history of low-perched, transgressive dune complexes along the southeastern shore of Lake Michigan

Abstract A general geomorphic history of low-perched coastal dunes along southeastern Lake Michigan is developed by combining new chronological data from P.J. Hoffmaster and Warren Dunes State Parks (SP) with published data from Van Buren SP, Silver Lake SP and dunes near Holland, Michigan. Fragmentary evidence of dunes older than 6 ka has been almost obliterated by active dune growth since the mid-Holocene Nipissing transgression of ancestral Lake Michigan. Aeolian activity continued during the drop from peak water levels ∼4.7 ka resulting in broad fields of low dunes. Aeolian activity halted during a period of low lake levels but was renewed with the development of large parabolic dune during the Algoma high-water phase of Lake Michigan at ∼3.2 ka. This was followed by reduced aeolian activity and development of the Holland Paleosol. Subsequent dune remobilization predates European settlement. High lake levels and land use practices cannot completely account for the pattern of aeolian activity which may be affected by changes in storm winds linked to changes in the paths of extratropical cyclones. Dune field morphology depends on the whether the shore is receding, prograding or stable. Simple lake-plain complexes form along receding shorelines where lakefront erosion exposes sediment to aeolian transport, leading to the preservation of a single set of large parabolic dunes migrating eastward with the shoreline. Compound lake-plain complexes form along stable or prograding shorelines. Here progressively younger dune ridges develop and blowouts migrate inland forming overlapping and nested parabolic dunes.

Coastal Sediment Dynamics and River Discharge as Key Factors Influencing Coastal Ecosystem Productivity in Southeastern Lake Michigan

Coastal Sediment Dynamics and River Discharge as Key Factors Influencing Coastal Ecosystem Productivity in Southeastern Lake Michigan

The Holland Paleosol: an informal pedostratigraphic unit in the coastal dunes of southeastern Lake Michigan

A very prominent buried soil crops out in coastal sand dunes along an ~200 km section of the southeastern shore of Lake Michigan. This study is the first to investigate the character of this soil — informally described here as the Holland Paleosol — by focusing on six sites from Indiana Dunes National Lakeshore north to Montague, Michigan. Most dunes in this region are large (&gt;40 m high) and contain numerous buried soils that indicate periods of reduced sand supply and comcomitant stabilization. Most of these soils are buried in the lower part of the dunes and are thin Entisols. The soil described here, in contrast, is relatively well developed, is buried in the upper part of many dunes, and formed by podzolization under forest vegetation. Radiocarbon dates indicate that this soil formed between ~3000 and 300 calibrated years BP. Pedons of the Holland Paleosol range in development from thick Entisols (Regosols) with A–Bw–BC–C horizonation to weakly developed Spodosols (Podzols) with A–E–Bs–Bw–BC–C profiles. Many profiles have overthickened and (or) stratified A horizons, indicative of slow and episodic burial. Differences in development are mainly due to paleolandscape position and variations in paleoclimate among the sites. The Holland Paleosol is significant because it represents a relatively long period of landscape stability in coastal dunes over a broad (200 km) area. This period of stability was concurrent with numerous fluctuations in Lake Michigan. Given the general sensitivity of coastal dunes to prehistoric lake-level fluctuations, the soil may reflect a time when the lake shore was farther west than it is today. The Holland Paleosol would probably qualify as a formal pedostratigraphic unit if it were buried by a formal lithostratgraphic or allostratigraphic unit.

Spring phytoplankton photosynthesis, growth, and primary production and relationships to a recurrent coastal sediment plume and river inputs in southeastern Lake Michigan

A recurrent coastal sediment plume (RCP) is an episodic event in the southern basin of Lake Michigan that typically coincides with the spring diatom bloom. Strong winter storm activity during El Niño conditions in 1998 resulted in a large and intense RCP event. Consistently higher values of the light‐saturated rate of photosynthesis, PmaxB, were observed in spring 1998 compared to 1999 and 2000. Higher values of PmaxB in 1998 appeared to be related to increased availability of phosphorus, as evidenced by significant correlations of PmaxB with soluble reactive phosphorus (SRP). Light‐saturated growth rates were also significantly correlated with SRP concentrations. These findings were consistent the view that the RCP was a source of enrichment. However, incubation experiments involving lake water enriched with sediments showed relatively small increases in growth and photosynthetic parameters, while enrichments with river water exhibited elevated rates. This result, along with increased levels of river discharge in 1998 and high levels of dissolved phosphorus in river water, supported the view that riverine inputs rather than the RCP were responsible for the higher photosynthetic parameters and growth seen for coastal margin assemblages. Despite the higher levels of PmaxB in 1998, model analyses revealed that reduced light availability resulting from the intense RCP event constrained phytoplankton growth rates and primary production during this season and apparently suppressed the development of a typical spring bloom. These findings indicate a potential for reduced ecosystem productivity in response to extreme storm events, the frequency of which may increase with projected long‐term climate changes.