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Salt marshes along many tidal systems in New England have been ditched since colonial times. These ditches have been thought to help control mosquito populations and increase salt marsh hay production by improving water drainage from the marsh. Although these ditches are prominent geomorphic features, little quantitative work has focused on how these man-made ditches may alter marsh hydrology and geomorphology. This study attempts to quantify the ways in which ditches alter sediment and water transport pathways and how that affects the overall morphology and surface geology. This study also addresses treatment affects on sedimentation from fertilization and fish removal associated with the NSF funded TIDE project. Short-term sediment deposition rates and relative elevations were determined for ditched and non-ditched marsh areas in four tidal creeks along the Rowley River in the summers of 2003, 2004, 2005, and 2006. Total suspended solids samples were also collected in the creek channels adjacent to the marsh areas sampled. Marsh surface samples for grain size analysis and organic content were collected as well. To quantify flow patterns, a grid system of stakes was set up on the marsh platform of two creek systems and water height was measured relative to these stakes over the course of a tidal cycle. This allowed for a better determination of the areas that flooded first and how long water stayed on the marsh platform in ditched and non-ditched areas. Measurements of marsh platform elevation indicated that the interior regions of ditched areas stand significantly lower than non-ditched areas. In ditched marsh areas, the hydrologic data demonstrated that the interior regions of the marsh were typically flooded first and stayed flooded longer. Non-ditched regions instead were flooded only after the water had topped the creek bank. As a result of these modified flow pathways, classic patterns of sedimentation and of organic matter and grain size distribution occurred less often in ditched marsh areas relative to non-ditched areas. In contrast to non-ditched marsh platforms, ditched platforms commonly had areas of increased deposition, decreased organic matter and increased grain size in innermost marsh areas. Although the absolute magnitude of deposition was similar with or without ditches, deposition in ditched areas was somewhat less responsive to the classic control of hydroperiod. Possible explanations for lower platform elevation in ditched marshes include (i) trapping of suspended sediment in ditches and (ii) enhancement of sediment export associated with the short distance from platform to ditch. The former is consistent with observations of lower concentration in ditches relative to natural creeks, and the latter is consistent with observations of coarser grain size and lower organic content observed on ditched marshes relative to non-ditched marshes. A longer hydroperiod and lower elevation in ditched areas would then be required at equilibrium to enhance net deposition so that accretion could keep up with relative sea level rise. The similar observed magnitudes of deposition in ditched and non-ditched areas supports the conclusion that the lower elevation of ditched platforms is in quasi-equilibrium with the higher elevations of non-ditched areas. Other results of this study include a demonstration of the high (1-2 cm) accuracy of the tide stick method for measuring marsh elevation, the finding that short term source of marsh sediment is primarily internal cycling, and the finding that fertilizing creeks systems and removing fish have no significant effects on short term sediment concentration, sediment delivery, sedimentation, inorganic sediment properties or marsh elevation.

Natural coastal habitats throughout Chesapeake Bay are increasingly threatened with shoreline modification due to population growth and rising rates of development. The replacement of these natural coastlines with hardened structures such as seawalls (bulkheads) and stone revetments (riprap) not only compromises vegetation at the land-water interface, but also can influence several elements of local aquatic food webs. Effects of these alterations have been well-studied with respect to fish assemblages and intertidal communities, particularly in conjunction with larger-scale watershed development, and recently, interest has shifted toward investigation of the effects of shoreline development on subtidal benthic infaunal communities.This study evaluated the direct, local impacts of bulkhead and riprap compared to natural marsh shorelines, as well as the effects of sediment characteristics, predator abundance, and system-specific physical features on benthic infauna in the Patuxent River, Chesapeake Bay. Forty-five sites were divided among three shoreline types and distributed across three main river zones. At each site, a benthic infaunal suction sample (3-mm mesh), push-core sample (500-μm mesh), sediment samples, water-quality measurements, and trawls for predators were taken. Samples were sorted to determine density, diversity, and biomass of infaunal organisms. Data were assessed using an Information-Theoretic approach (AIC analysis) to determine the most influential variables, of those measured, on the infaunal community for two benthic data sets: 3-mm-suctions and 500-μm-cores. Results from these analyses on 3-mm samples suggested that shoreline type was the best predictor of diversity, while wave energy, sediment chlorophyll concentration, sediment type, and predator abundance best predicted density and biomass. Benthic responses within the 500-μm dataset were not strongly affected by shoreline type. Rather, responses were best predicted by sediment chlorophyll, wave energy, sediment type, predator abundance, and sediment organic carbon (TOC) content.Results indicate that, compared to other Bay tributaries, the Patuxent River is a relatively degraded system. The small range in long-term responses of Patuxent infauna from previous work provides a possible explanation as to why I was unable to see significant differences in infaunal response among shoreline types in the current study (i.e., there was little scope for change by shoreline in the system as a whole). However, I suggest that natural marsh habitats are healthier subsystems of the Patuxent River, due to the greater variety of infaunal feeding guilds and higher infaunal biomass observed at these compared to hardened sites. Higher predator abundance was associated with higher infaunal biomass at natural marsh sites in both size fractions, suggesting the bottom-up control of higher-trophic-level species in this system, as predators seek out suitable prey items. Given these observations, and the fact that influential variables such as wave energy, sediment nutrient and chlorophyll content, predator abundance, and sediment type may vary according to shoreline type, the replacement of natural shoreline with hardened structures will lead to complex changes in subtidal benthic communities in Chesapeake Bay tributaries and should be minimized to maintain qualities of the natural system.

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Point source controls have been the primary methodology utilized to reduce pollutant loads into the waterways of the United States for the last 30 years. However, the complex dynamics that occur in the water column, in conjunction with increased amounts of urbanization in our watersheds, have made point source controls alone inadequate for solving our nation’s water quality problems. In order to determine the impacts that various water quality management strategies will have on water quality, dynamic models capable of simulating the complex interactions in both the water column and the watershed are necessary. The Blackstone River Water Quality Study was implemented to determine the impact of ongoing and proposed upgrades at wastewater treatment plants on water quality along the Blackstone River and the magnitude of corresponding reductions in pollutant loads into Narragansett Bay. The impacts of changes in land use in the surrounding watershed on water quality in the Blackstone were also analyzed as part of the study. The study utilizes an HSPF hydrologic model developed for the Blackstone River by the USGS. UMass and CDM then added water quality simulation capabilities to the model as well as discretizing the mainstem and extending its simulation period. The model continuously simulates water quantity and quality across 100+ reaches used to model the Blackstone River watershed for the period from 1996-2007. As part of the study, the construction, calibration and error bound of the model are detailed as well. Based on the results of model simulations, it is shown that improvements in instream water quality as well as decreases in the downstream pollutant transport are achieved through ongoing and proposed point source control strategies. However, it has also been shown that non-point source controls can also achieve the same instream improvement and pollutant reduction as the proposed point source controls in the watershed. Despite the significant improvements in water quality observed during the model simulations, none of the pollution reduction strategies, including the removal of all point source loads from the system allow the Blackstone River to achieve ambient water quality standards as recommended by the U.S. Environmental Protection Agency.

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