Shimon Anisfeld

ABSTRACT Purpose Sediment fingerprinting with elemental tracers is widely used to identify sources of sediment to rivers. However, due to the need to isolate large amounts of suspended sediment, this approach can be difficult to implement in remote locations, such as the Mara River in Kenya, where high (and increasing) sediment loads are of concern. Materials and methods We report several innovations that allowed us to carry out sediment fingerprinting in a portion (>6,500 km2) of the Mara River Basin. First, we utilized sediment-laden filters (sediment mass ∼0.1 g) for our river samples, rather than the traditional approach of extracting >1 g of sediment from large volumes of water. This allowed us to easily collect flow-weighted samples, and to process and analyze samples without access to centrifugation equipment. We carried out extensive quality control tests to ensure that we could reproducibly measure elemental concentrations of sediment trapped on filters. Second, we modified a readily available Bayesian inference mixing model (Stable Isotope Analysis in R) to create source signatures and to apportion downstream samples to sources. Third, we included hippo feces as a potential source, given the critical role that large wildlife plays in this ecosystem. Results and discussion We found that: (1) sediment captured by filtration can be digested and analyzed reproducibly and used in sediment fingerprinting; (2) our four sources (three geographic categories and hippo feces) were reasonably well-separated in their signatures; (3) the three sub-basins all contributed substantially to sediment loading in the Mara; and (4) hippo feces contributed a small, but measurable, proportion of sediment in this system. Conclusions Sediment-laden filters can be used successfully in identifying sediment sources through fingerprinting. The modified method of sediment fingerprinting should prove useful in other remote river basins. Our results support the hypothesis that the Upper Mara is important in supplying sediments to the river, while also highlighting the Talek sub-basin as a major contributor.

We synthesized existing data on chemical contaminants in Long Island Sound (LIS) from published reports and unpublished databases. We found several cases of systematic differences between data sources, which complicated the tasks of understanding the health of LIS and of identifying trends over time. Of the three media examined—water, sediment, and biota—sediment (especially in western LIS) most often exhibited pollutant

ABSTRACT The restriction of tidal flow to salt marshes, a common phenomenon in densely populated coastal areas, leads to marked changes in the hydrologic regime of the marsh, which can in turn pose water quality problems both within the marsh and for the larger estuary. We have found significant differences in marsh chemistry and water quality between a tide-gated (restricted flow) marsh and a nearby, unrestricted reference marsh. During the summer of 1995, the desiccation of the restricted marsh due to operation of the tide gate led to a disconnection among the sediments, the small drainage ditches, and the main channel. This allowed dramatic changes to take place in sediment chemistry, including lowered alkalinity and elevated nutrient levels. Re-connection of the sediments with the surface water as a result of rainstorms led to two episodes of severe acidification (pH 3−4) as well as to increases in surface water nitrogen concentrations. Clean-technique trace metal measurements showed that the acidic conditions led to mobilization of Pb, Cu, Ag, and Cd, with extremely high levels observed in the dissolved phase (>2000 ng/L dissolved Pb). Sulfide, sulfate, and chloride measurements indicated that the acidification was most likely the direct result of desiccation-induced oxidation of the reduced sulfide (e.g., pyrite) that had accumulated in the sediments. The seasonal operation of the tide gate in this marsh may contribute to the potential for acidification. In contrast to observations in other restricted marshes, low dissolved oxygen (DO) does not seem to be a problem in the restricted marsh:  DO concentrations were higher than in the reference marsh. The two marshes differed in the distribution of plant species but not in productivity or C:N ratios for a given species.