Sources of Suspended-Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model1

Brakebill, John W., Scott W. Ator, and Gregory E. Schwarz, 2010. Sources of Suspended-Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model. Journal of the American Water Resources Association (JAWRA) 46(4): 757-776. DOI: 10.1111/j.1752-1688.2010.00450.x Abstract: We describe the sources and transport of fluvial suspended sediment in nontidal streams of the Chesapeake Bay watershed and vicinity. We applied SPAtially Referenced Regressions on Watershed attributes, which spatially correlates estimated mean annual flux of suspended sediment in nontidal streams with sources of suspended sediment and transport factors. According to our model, urban development generates on average the greatest amount of suspended sediment per unit area (3,928 Mg/km²/year), although agriculture is much more widespread and is the greatest overall source of suspended sediment (57 Mg/km²/year). Factors affecting sediment transport from uplands to streams include mean basin slope, reservoirs, physiography, and soil permeability. On average, 59% of upland suspended sediment generated is temporarily stored along large rivers draining the Coastal Plain or in reservoirs throughout the watershed. Applying erosion and sediment controls from agriculture and urban development in areas of the northern Piedmont close to the upper Bay, where the combined effects of watershed characteristics on sediment transport have the greatest influence may be most helpful in mitigating sedimentation in the bay and its tributaries. Stream restoration efforts addressing floodplain and bank stabilization and incision may be more effective in smaller, headwater streams outside of the Coastal Plain.     

Significance of Riverine Hypoxia for Fish: The Case of the Big Sunflower River,Mississippi1

Shields, F. Douglas, Jr. and Scott S. Knight, 2011. Significance of Riverine Hypoxia for Fish: The Case of the Big Sunflower River, Mississippi. Journal of the American Water Resources Association (JAWRA) 48(1): 170‐186. DOI: 10.1111/j.1752‐1688.2011.00606.x Abstract: Degraded streams draining low‐relief, intensively cultivated watersheds may experience periods of hypoxia or anoxia. A three‐year study of water chemistry, fish, and physical habitat in the Big Sunflower River in northwestern Mississippi coupled with continuously logged physicochemical and hydrology data provided by others showed prolonged periods of hypoxia associated with higher flows. Fish species richness was directly related to dissolved oxygen (DO) concentration (r² = 0.35, p = 0.00004), and ordination using nonmetric multidimensional scaling (NMS) indicated strong association between fish community structure and DO. Low‐head weirs supported relatively dense and diverse fish communities and thus provided local habitat enhancement, but may create stagnant zones upstream due to backwater effects that exacerbate low DO problems. Although hypoxia has been reported for some lightly degraded rivers and floodplains, our observations suggest hypoxia in Big Sunflower River and similar systems alters fish species composition and should be remediated. Cost‐effective remediation will require better understanding of autotrophic and heterotrophic processes that control DO and the relationship of these processes to discharge.     

Vulnerability of Fraser River sockeye salmon to climate change: A life cycle perspective using expert judgments

Fraser River sockeye salmon have been the basis for a major commercial fishery shared by Canada and the United States, and an important cultural foundation for many aboriginal groups; they are also of huge ecological significance throughout the Fraser Basin. The potential for altered aquatic habitat and temperature regimes due to climate change is an important concern for Fraser River sockeye salmon. This paper characterizes the vulnerability of Fraser River sockeye salmon to future climate change using an approach that is novel on three counts. First, previous efforts to assess the vulnerability of salmon to climate change have largely focused on only part of the life cycle, whereas we consider climate vulnerability at all stages in the life cycle. Second, we use the available scientific literature to provide a basis for structuring and eliciting judgments from fisheries science and management experts who research and manage these systems. Third, we consider prospects for mitigating the effects of climate change on sockeye salmon. Tests showed that participants’ judgments differentiated in statistically significant ways among questions that varied in terms of life stages, spawning regions and climate scenarios. The consensus among participants was that Fraser River sockeye are most vulnerable to climate change during the egg and returning adult stages of the life cycle. A high temperature scenario was seen as imposing the greatest risk on sockeye stocks, particularly those that migrate to the upper reaches of the Fraser River system and spawn earlier in the summer. The inability to alter water temperature and the highly constrained nature of sockeye management, with competing gear types and sequential fisheries over a long distance, suggest the potential to mitigate adverse effects is limited. Fraser River sockeye already demonstrate a great deal of adaptive capacity in utilizing heterogeneous habitats in different river sub-basins. This adaptability points to the potential value of policies to make stocks more resilient to uncertain futures.     

The effect of pH on metal accumulation in two Alyssum species

Nickel phytoextraction using hyperaccumulator plants offers a potential for profit while decontaminating soils. Although soil pH is considered a key factor in metal uptake by crops, little is known about soil pH effects on metal uptake by hyperaccumulator plants. Two Ni and Co hyperaccumulators, Alyssum murale and A. corsicum, were grown in Quarry muck (Terric Haplohemist) and Welland (Typic Epiaquoll) soils contaminated by a Ni refinery in Port Colborne, Ontario, Canada, and in the serpentine Brockman soil (Typic Xerochrepts) from Oregon, USA. Soils were acidified and limed to cover pH from strongly acidic to mildly alkaline. Alyssum grown in both industrially contaminated soils exhibited increased Ni concentration in shoots as soil pH increased despite a decrease in water-soluble soil Ni, opposite to that seen with agricultural crop plants. A small decrease in Alyssum shoot Ni concentration as soil pH increased was observed in the serpentine soil. The highest fraction of total soil Ni was phytoextracted from Quarry muck (6.3%), followed by Welland (4.7%), and Brockman (0.84%). Maximum Ni phytoextraction was achieved at pH 7.3, 7.7, and 6.4 in the Quarry, Welland, and Brockman soils, respectively. Cobalt concentrations in shoots increased with soil pH increase in the Quarry muck, but decreased in the Welland soil. Plants extracted 1.71, 0.83, and 0.05% of the total soil Co from Welland, Quarry, and Brockman, respectively. The differences in uptake pattern of Ni and Co by Alyssum from different soils and pH were probably related to the differences in organic matter and iron contents of the soils.