Response of three paleo-primary production proxy measures to development of an urban estuary.

In this study we present a novel comparison of three proxy indicators of paleoproductivity, pigments, biogenic silica (BSi), and cysts of autotrophic dinoflagellates measured in cored sediments from New Bedford Harbor, Massachusetts. In addition to detailed historical reports we use palynological signals of land clearance, changes in the ratio of centric and pennate diatoms, sedimentary organic carbon and stable carbon isotopes to constrain our interpretations. Our study spans the period from prior to European settlement to approximately 1977, during which watersheds were cleared, port development occurred and much of the coastal property became industrialized. The combined effects of nutrient loading from watershed clearance and urban sewage on the estuarine ecosystem shifted not only levels of primary production, but also the nature of the production. Our proxies show that when European colonists first arrived the estuarine production was benthic-dominated, but eventually became pelagic-dominated. Importance of water column production (by diatoms and dinoflagellates) rapidly increased as soil nitrogen was released following forest clearance. Stabilization in rates of forest clearance is reflected as a decline in production. However, population increases in the urbanizing watershed brought new sources of nutrients through direct sewage discharge, apparently again stimulating primary production. We assume that early 20th century changes in sewage discharge and introduction of heavy metals into Harbor waters caused a temporary reduction in primary production. The introduction of a new sewer outfall near the core site and changes in estuarine hydrography due to construction of a hurricane barrier across the mouth of the harbor are reflected by renewed water column production, but decreases in the population of diatoms and dinoflagellates. Fossil pigments suggest renewed water column production in the latest years recorded by our sediment core.

An inventory of historical mercury emissions in maritime canada: implications for present and future contamination.

Mercury is a longstanding concern in Maritime Canada due to high levels of contamination in a number of fish and bird species. The recycled component of past releases of anthropogenic mercury may be a significant source of ongoing pollution in many areas. Historical information on mercury releases can be used to quantify past and present anthropogenic contamination. We present an inventory of historical mercury emissions from anthropogenic sources in Maritime Canada for the years 1800-1995. Long-term trends in mercury emissions and the significance of the cumulative burden of mercury released from local sources are discussed. Emissions are calculated using both historical monitoring data and the application of emission factors. The nature of current anthropogenic sources of mercury is quite different than it was several decades ago when many of the existing policies governing mercury pollution were created. Our inventory illustrates that many of the most significant sources in the past such as the chlor-alkali industry, paint containing mercury additives, and pharmaceuticals, have been largely phased out with fossil fuel combustion and waste disposal remaining as the most significant modern sources. Atmospheric emissions in Maritime Canada peaked in 1945 (> 1,750 kg year-1), and again between 1965 and 1970 (> 2,600 kg year-1). Cumulative releases of mercury from anthropogenic sources for the years 1800-1995 were between 115 and 259 t to the atmosphere alone, and 327-448 t when discharges to wastewater and effluents were included. Assuming that only 0.2% (Nriagu, 1994.) of these releases become part of the recycled fraction of current fluxes, we estimate that between 570 and 900 kg Hg year-1 is deposited in Maritime Canada from past anthropogenic sources. Modern sources within Maritime Canada contribute at least 405 kg year-1 to the total annual deposition of 1.71 t over the provinces of New Brunswick, Nova Scotia and Prince Edward Island, leaving approximately 735 kg year-1 from natural sources and long-range contamination. Further study is needed to verify these estimates and clarify the significance of natural and long-range sources of mercury in Maritime Canada.

The history of mercury emissions from fuel combustion in Maritime Canada.

In this study, we present an inventory of historical emissions of mercury resulting from combustion of wood, coal and refined petroleum products in Maritime Canada. The pattern of emissions illustrates the strong influences of population growth, industrial development and prevailing fuel preferences in the region. According to our calculations, anthropogenic mercury releases from fuel combustion in Maritime Canada have cumulatively totaled more than 50 tonnes since 1800. We have compiled both high and low estimates of annual mercury releases in this region. Mercury emissions from fuel combustion in Maritime Canada reached a maximum level in the 1940s. At this time, emissions were between 778 (low) and 1494 (high) kg per year, coinciding with the period of most intensive coal use in Maritime Canada. In 1995, emissions were approximately 54% of the level reached in 1940, at 427 (low)-800 (high) kg per year. In presenting this emissions inventory, we hope to refine past estimates with current information on the mercury content of different fuel types, and create a comprehensive database on how mercury emissions from various sources have changed over time.

An inventory of 13C abundances in coastal wetlands of Louisiana, USA: vegetation and sediments.

Organic carbon-rich sediments from the surface of fresh, intermediate, brackish and salt marshes of coastal Louisiana were sampled and analyzed for their 13C content. The average ∂13C from all sites within each wetland type was-27.8‰,-22.1‰,-16.9‰, and-16.2‰, for fresh, intermediate, brackish and salt marshes, respectively. Means from the fresh, intermediate and brackish marshes were significantly different at the 0.01 level. A mixing model using measurements of standing crop and ∂13C of plant carbon was applied to estimate the contribution of each species to the sedimentary carbon at four of the marsh sites. Sedimentary ∂13C values generally reflected that of the dominant species present at each site. Brackish and salt marsh samples, however, showed a negative shift of ∂13C with respect to whole plant carbon. We interpret these depeleted ∂13C values to be the result of more extensive organic matter decomposition and selective preservation of 13C-depleted refractory components in sediments from saline sites. The results of this study suggest that ∂13C composition of sedimentary carbon may offer a valuable tool for distinguishing subtle changes in paleohydrology of wetlands resulting from relative sea level changes.