Margaret B. Lansing

Trends in the Benthic Macroinvertebrate Community of Saginaw Bay, Lake Huron, 1987 to 1996: Responses to Phosphorus Abatement and the Zebra Mussel, Dreissena polymorpha

Trends in benthic macroinvertebrate populations were examined in inner and outer Saginaw Bay, Lake Huron, from 1987 to 1996. These years represent the time period after phosphorus abatement, but immediately before (1987 to 1990) and after (1991 to 1996) colonization of the bay by the zebra mussel, Dreissena polymorpha. In 1987 to 1990, densities of the major macroinvertebrate groups in the inner and outer bay were not significantly different from, or were greater than, densities reported just prior to abatement efforts in the early 1970s. Oligochaete densities in the deepwater/silt region of the inner bay were trending downward between 1988 and 1991, but pollution-tolerant forms dominated the community, indicating the system was eutrophic just prior to Dreissena colonization. Dreissena impacts on the macroinvertebrate community varied depending on the particular habitat. At shallow-water/sand sites in the inner bay, Gammarus increased, and sphaeriids declined after Dreissena colonization, but no changes were observed in oligochaetes and chironomids, and overall species diversity showed little change. At deepwater/silt sites in the inner bay, densities of oligochaetes and chironomids declined just after the peak in Dreissena, but then returned to levels generally similar to those found prior to Dreissena. The oligochaete trophic index at deepwater/silt sites indicated a shift from eutrophic to more oligotrophic indicator species after Dreissena became established, and species diversity increased. In the outer bay, Diporeia and sphaeriids declined after Dreissena peaked, but few other changes were observed. Total non-dreissenid macroinvertebrate biomass (AFDW) in the inner bay, and in shallow areas of the outer bay, did not change as a result of Dreissena colonization. On the other hand, biomass in the deeper regions of the outer bay decreased because of the loss of Diporeia. Changes in the inner and outer bay typify the growing dichotomy between nearshore and offshore in the Great Lakes since Dreissena became established.

Development of recurrent coastal plume in Lake Michigan observed for first time

NOAA CoastWatch satellite imagery from early 1996 captured the initiation, development, and decay of a recurrent coastal plume in southern Lake Michigan (Figure 1). For the past 4 years intermittent satellite coverage has revealed a late winter-early spring plume in the lake, a feature also observed by Mortimer [1988]. In 1996, clear weather conditions allowed researchers to observe the plumes development for the first time and they also collected water samples from helicopter and a small boat.

Particle Transport, Nutrient Cycling, and Algal Community Structure Associated with a Major Winter-Spring Sediment Resuspension Event in Southern Lake Michigan

Abstract Over the past decade, intermittent satellite imagery revealed the presence of an extensive plume of resuspended sediments in late winter-early spring with a clear offshore projection coinciding with the region of maximum sediment accumulation in the lake. The large scale of the plume implied that this process was important in sediment, and associated constituent, cycling and transport, but it had never been sampled due to severe conditions. The onset of the 1996 event coincided with a major March storm. Within a few days the plume was approximately 10 km wide and over 300 km in length, implying that the source of the reflective materials was widely distributed. An estimate of the total mass of resuspended sediment, 12 days after the storm, was similar to the annual external load of (sand-free) particulate material to the southern basin. The high turbidity plume persisted for over a month, progressing northward along the eastern shore with a major offshore transport feature. Sediment traps within this feature recorded a major mass flux event. The plume was sampled on two occasions and was found to contain 5 to 10 times as much suspended matter as open-lake locations outside the visible plume. Total particulate phosphorus was high within the plume making this episodic process important in sedimentwater exchange. The diatom community structure within the plume was significantly different from outside the plume and was characteristic of more eutrophic waters. Abundance of non-diatom phytoplankton and microbial food web organisms were highest at the plume edge. The episodic nature of this process makes it difficult to sample, but the scale makes it important in designing monitoring programs and massbalance modeling efforts.

Catecholamines as Potential Sub-lethal Stress Indicators in Great Lakes Macrobenthic Invertebrates

Concentrations of the catecholamines [dopamine (D), and norepinephrine (NE)] were measured in representative Great Lakes macrobenthic invertebrates to determine the feasibility of using these compounds as indicators of sub-lethal stress. Epinephrine [E] was not detected in most of these invertebrates. A high performance liquid chromatographic procedure was modified for use with aquatic invertebrates. Chironomids and oligochaetes contained D concentrations that were similar, averaging 1 pmole/mg wet wt. Crustacean D levels were lower, averaging 0.2 pmole/mg wet wt. NE averaged 0.2 pmole/mg wet wt. for chironomids and 0.57 pmole/mg wet wt. for oligochaetes. NE was not detected in the crustaceans. Individual chironomids contained detectable levels of catecholamines; all other invertebrates required pooled homogenates. The chironomid group was targeted for laboratory stress experiments. Cultured midge larvae (Chironomus tentans) subjected to acute thermal stress (35°C) exhibited D concentrations significantly lower than controls (23°C). Animals exposed to lindane concentrations 0.5 mg/L - 8.0 mg/L contained D concentrations significantly higher than controls. NE and E were not detected in either stress experiment. Demonstration of dramatic catecholamine concentration changes in response to stressors suggests that these compounds could potentially be indicators of sublethal stress.