Effects of Sedimentation and Turbidity on Lotic Food Webs: A Concise Review for Natural Resource Managers

Abstract

Abstf'~ct: Sedimentation and turbidity are significant contributors to declines in populations of North American aquatic organisms. Impacts to lotic fauna may be expressed through pervasive alterations in local food chains beginning at the primary trophic level. Decreases in primary production are associated with increases in sedimentation and turbidity and produce negative cascading effects through depleted food availability to zooplankton, insects, freshwater mollusks, and fish. Direct effects at each trophic level are mortality, reduced physiological function, and avoidance; however, decreases in available food at trophic levels also result in depressed rates of growth, reproduction, and recruitment. Impacts of turbidity to aquatic organisms often seem inconsistent among watersheds and experiments, but this apparent difference is actually due to the lack of correlation between suspended sediment concentrations (mg/L) and units of measure (Nephelometric Turbidity Units, NTU). The use of NTU as a surrogate measurement of suspended sediment to predict biotic effects within watersheds is dubious. Similar NTU measurements from different watersheds may be correlated with different concentrations of suspended sediment. For monitoring the effects of turbidity within local watersheds, we recommend that the correlation between suspended sediment and NTUs be examined over a range of discharge recordings, and that this be used as a baseline to examine local effects. We recommend that riparian buffer strips and livestock fencing be used to reduce sediment input to streams.

Relationships between water transparency and abundance of Cynodontidae species in the Bananal floodplain, Mato Grosso, Brazil

“…In such conditions, the decrease of water transparency occurs mainly due to the waters originating from tributaries that drain large deforested areas, which leads to increased transport of sediments by surface runoff, increasing water turbidity. This increase in turbidity reduces the availability of light in the environment and alters substantially visual activities such as foraging and finding mates (Matthews, 1998;Henley et al, 2000). In addition, it is possible that higher turbidity can also be occurring through eutrophication of the aquatic habitats, due to the loading of nutrients coming from areas occupied by agriculture and ranching or due to the greater amount of light reaching the water surface due to the reduction in riparian vegetation.…”

“…Increasing water turbidity and consequently decreasing transparency has several effects on fish fauna composition and structure (Henley et al, 2000;Lin & Caramaschi, 2005). These growing environmental problems are intensified by the paucity of studies on fish fauna in this biome, especially in Mato Grosso, the Brazilian state which holds the larger extension of nonmodified Cerrado areas (Silva et al, 2006).…”

Interactions between macroinvertebrate taxa and complex environmental gradients influencing abundance and distribution in the Umatilla River, Northeastern Oregon

“…Increased suspended solids in the water column limits the availability of light for primary production, which can then impact primary consumers and potentially alter the food web interactions at higher trophic levels. Increased turbidity is associated with a decrease in the diversity of macroinvertebrates as well as decreases in fish species richness, predation, and reproductive success (Lloyd et al 1989;Henley et al 2000; Van de Meutter et al 2005). According to the Oregon Department of Environmental Quality, the Umatilla River exceeds benchmarks in turbidity measurements, making it water quality limiting (ODEQ 2001).…”

The influence of the landscape structure within buffer zones, catchment land use and instream environmental variables on mollusc communities in a medium‐sized lowland river

“…Increased sedimentation and turbidity affect the lotic food webs, e.g. by decreasing the filtration rate of bivalves, thereby causing them to starve (Henley et al 2000). Hence, the clear negative correlation between the distribution of prosobranch species and gill-breathing fingernail clams and turbidity may be explained by their physiological make-up.…”