A diatom-based transfer function was used to reconstruct water chemistry before European settlement in 55 Minnesota lakes. The lakes span three natural ecoregions, which differ in their history of land use, as well as in surficial geology, climate, and vegetation. Postsettlement trends were compared with water chemistry change reconstructed from two presettlement core sections (circa 1750 and 1800) as a measure of natural variability. Presettlement water quality changes were generally small and nondirectional in all three ecoregions. In contrast, half of the urban lakes showed a statistically significant increase in chloride, whereas 30% of urban and 30% of agricultural region lakes record a statistically significant increase in total phosphorus between 1800 and the present. These changes, which are attributed to road salt and nutrient runoff, are strongly correlated with the percentage of watershed area that is developed (residential or urban) in the case of chloride increases and the percentage of developed (metropolitan areas) or agricultural (agricultural areas) land in the case of nutrient increases. Water quality has changed little since 1800 for lakes in the forested regions of northeastern Minnesota. The few changes that are seen in this region are likely related to natural variations in climate or catchment soils.Résumé : L'utilisation d'une fonction de transfert basée sur les diatomées nous a permis de reconstituer la chimie des eaux dans cinquante-cinq lacs du Minnesota avant l'établissement des européens. Les lacs se répartissent dans trois écorégions naturelles qui différent par l'utilisation que l'on a fait des terres dans le passé, ainsi que par la géologie de surface, le climat et la végétation. Nous avons comparé les tendances qui sont apparues après la colonisation avec les changements estimés à partir de deux sections de carottes datant d'avant la colonisation (vers 1750 et 1800) qui repré-sentent la variabilité naturelle. Avant la colonisation, les changements de la qualité de l'eau dans les trois écorégions étaient généralement faibles et sans tendance marquée particulière. En revanche, entre 1800 et l'époque actuelle, la moitié des lacs urbains affichent une augmentation statistiquement significative des chlorures et 30 % des lacs urbains et 30 % des lacs des régions agricoles subissent une augmentation statistiquement significative du phosphore total. Il existe une forte corrélation entre ces changements, qui sont attribuables à l'apport du sel routier et de nutriments par ruissellement, avec le pourcentage des terres du bassin versant qui sont urbanisés (résidentielles ou urbaines) dans le cas de l'augmentation des chlorures ou alors développées (régions métropolitaines) ou exploitées pour l'agriculture (zones agricoles) dans le cas de l'augmentation des nutriments. Dans les régions forestières du nord-est du Minnesota, la qualité des eaux des lacs a peu varié depuis 1800. Les quelques changements observés dans cette région sont vraisemblablement reliés aux variations naturelles...

Abstract. The Barnegat Bay-Little Egg Harbor Estuary is classified here as a highly eutrophic estuary based on application of the National Oceanic and Atmospheric Administration's National Estuarine Eutrophication Assessment model. Because it is shallow, poorly flushed, and bordered by highly developed watershed areas, the estuary is particularly susceptible to the effects of nutrient loading. Most of this load (;50%) is from surface water inflow, but substantial fractions also originate from atmospheric deposition (;39%), and direct groundwater discharges (;11%). No point source inputs of nutrients exist in the Barnegat Bay watershed. Since 1980, all treated wastewater from the Ocean County Utilities Authority's regional wastewater treatment system has been discharged 1.6 km offshore in the Atlantic Ocean. Eutrophy causes problems in this system, including excessive micro-and macroalgal growth, harmful algal blooms, altered benthic invertebrate communities, impacted harvestable fisheries, and loss of essential habitat (i.e., seagrass and shellfish beds). Similar problems are evident in other shallow lagoonal estuaries of the Mid-Atlantic and South Atlantic regions. To effectively address nutrient enrichment problems in the Barnegat BayLittle Egg Harbor Estuary, it is important to determine the nutrient loading levels that produce observable impacts in the system. It is also vital to continually monitor and assess priority indicators of water quality change and estuarine health. In addition, the application of a new generation of innovative models using web-based tools (e.g., NLOAD) will enable researchers and decision-makers to more successfully manage nutrient loads from the watershed. Finally, the implementation of storm water retrofit projects should have beneficial effects on the system.

Abstract. Eutrophication of estuaries is an increasing global concern that requires development of new tools to identify causes, quantify conditions, and propose management options that address this environmental problem. Since eutrophication is often associated with increased inputs of land-derived nitrogen to estuaries, we developed NLOAD, a user-friendly, web-based tool that brings together six different published models that predict nitrogen loading to estuaries and two models that estimate nitrogen concentrations in coastal waters. Here we describe each of the models, demonstrate how NLOAD is designed to function, and then use the models in NLOAD to predict nitrogen loads to Barnegat Bay, New Jersey (USA). The four models that we used to estimate nitrogen loads to Barnegat Bay, when adjusted, all had similar results that matched well with measured values and indicated that Barnegat Bay receives roughly 26 kg NÁha . Atmospheric deposition was the dominant source of nitrogen to Barnegat Bay, followed by fertilizer nitrogen. Wastewater in Barnegat Bay is diverted to an offshore outfall and contributes no nitrogen to the system. The NLOAD tool has an additional feature that allows managers to assess the effectiveness of a variety of management options to reduce nitrogen loads. We demonstrate this feature of NLOAD through simulations in which fertilizer inputs to the Barnegat Bay watershed are reduced. Even modest cutbacks in the use of fertilizers on agricultural fields and lawns can be shown to reduce the amount of N entering Barnegat Bay.

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