Sphaerium

Abstract: Relationships between riparian land cover, in-stream habitat, water chemistry, and macroinvertebrates were examined in headwater streams draining an agricultural region of Illinois. Macroinvertebrates and organic matter were collected monthly for one year from three intensively monitored streams with a gradient of riparian forest cover (6, 22, and 31% of riparian area). Bioassessments and physical habitat analyses were also performed in these three streams and 12 other nearby headwater streams. The intensively monitored site with the least riparian forest cover had significantly greater percent silt substrates than the sites with medium and high forest cover, and significantly higher very fine organics in substrates than the medium and high forested sites. Macroinvertebrates were abundant in all streams, but communities reflected degraded conditions; noninsect groups, mostly oligochaetes and copepods, dominated density and oligochaetes and mollusks, mostly Sphaerium and Physella, dominated biomass. Of insects, dipterans, mostly Chironomidae, dominated density and dipterans and coleopterans were important contributors to biomass. Collector-gatherers dominated functional structure in all three intensively monitored sites, indicating that functional structure metrics may not be appropriate for assessing these systems. The intensively monitored site with lowest riparian forest cover had significantly greater macroinvertebrate density and biomass, but lowest insect density and biomass. Density and biomass of active collector-filterers (mostly Sphaerium) decreased with increasing riparian forest. Hilsenhoff scores from all 15 sites were significantly correlated with in-stream habitat scores, percent riparian forest, and orthophosphate concentrations, and multiple regression indicated that in-stream habitat was the primary factor influencing biotic integrity. Our results show that these "drainage ditches" harbor abundant macroinvertebrates that are typical of degraded conditions, but that they can reflect gradients of conditions in and around these streams.

Abstract: Big Lake is a shallow (mean depth = 0.89 m in 1973) 256-ha backwater lake on the floodplain of the Mississippi River in NE Iowa. During the summers of 1973 and 1974 Sphaerium and Hexagenia made up 81% of the benthic macroinvertebrate abundance and 92% of the benthic biomass; both taxa had greatly reduced abundance and biomass within stands of emergent Sagittaria along the lake margin. During July 1974 the Sagittaria net productivity was about 19 g/m/sup 2//day. Cesium-137 levels were determined in sediment samples showing that between 1896 and 1973 about 76 cm of sediment had accumulated in Big Lake, and the recent sedimentation rate (1964-1974) was about 1.7 cm/year. The calculated annual reduction in lake volume of about 37,400 m/sup 3//year suggests that the physical and biological components of this productive aquatic habitat will be greatly modified during the next few decades.

Abstract: The effects of particle concentration and season on the filtration rates of the freshwater clamSphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 µm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2–64 mg 1−1, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam−1 h−1. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams.