Identifying groundwater contributions to baseflow in a temperate headwater catchment

Inter-storm streamflow, or baseflow, is commonly assumed to be generated directly from groundwater discharge to the stream network. In moderate-relief terrain of New England, wetlands are important in stream function. The assumption that streamflow is generated from groundwater discharge from a headwater catchment containing 11% wetland or pond area coverage was tested using stable isotopes of water. Binary end-member mixing analysis showed that 18 to 30% of streamflow at the catchment outlet (less than 50% at 95% confidence) was generated from groundwater; the remainder was derived from outflow from an upstream wet meadow. Results from the wet meadow water and isotopic mass balance suggest \u3c27% of meadow outflow was accommodated by groundwater inflows. Increasing isotopic enrichment correlates more strongly with stream length within wetlands (p = 0.005) than catchment wetland area (p = 0.04); ranking catchments by the same metric also distinguishes catchments by their relative average run-off

A coupled terrestrial and aquatic biogeophysical model of the Upper Merrimack River watershed, New Hampshire, to inform ecosystem services evaluation and management under climate and land-cover change

Accurate quantification of ecosystem services (ES) at regional scales is increasingly important for making informed decisions in the face of environmental change. We linked terrestrial and aquatic ecosystem process models to simulate the spatial and temporal distribution of hydrological and water quality characteristics related to ecosystem services. The linked model integrates two existing models (a forest ecosystem model and a river network model) to establish consistent responses to changing drivers across climate, terrestrial, and aquatic domains. The linked model is spatially distributed, accounts for terrestrial–aquatic and upstream–downstream linkages, and operates on a daily time-step, all characteristics needed to understand regional responses. The model was applied to the diverse landscapes of the Upper Merrimack River watershed, New Hampshire, USA. Potential changes in future environmental functions were evaluated using statistically downscaled global climate model simulations (both a high and low emission scenario) coupled with scenarios of changing land cover (centralized vs. dispersed land development) for the time period of 1980–2099. Projections of climate, land cover, and water quality were translated into a suite of environmental indicators that represent conditions relevant to important ecosystem services and were designed to be readily understood by the public. Model projections show that climate will have a greater influence on future aquatic ecosystem services (flooding, drinking water, fish habitat, and nitrogen export) than plausible changes in land cover. Minimal changes in aquatic environmental indicators are predicted through 2050, after which the high emissions scenarios show intensifying impacts. The spatially distributed modeling approach indicates that heavily populated portions of the watershed will show the strongest responses. Management of land cover could attenuate some of the changes associated with climate change and should be considered in future planning for the region

Water Balance Model (WBM) Open Source Release Version 1.0.0 Ancillary Data

Download the Singularity image and data files associated with the open source release of the University of New Hampshire Water Balance Model from the the University of New Hampshire Water Balance Model Ancillary Data Download Websit

Controls of Chloride Loading and Impairment at the River Network Scale in New England

Chloride contamination of rivers due to nonpoint sources is increasing throughout developed temperate regions due to road salt application in winter. We developed a river-network model of chloride loading to watersheds to estimate road salt application rates and investigated the meteorological factors that control riverine impairment by chloride at concentrations above thresholds protective of aquatic organisms. Chloride loading from road salt was simulated in the Merrimack River watershed in New Hampshire, which has gradients in development density. After calibration to a regional network of stream chloride data, the model captured the distribution of regional discharge and chloride observations with efficiencies of 93 and 75%, respectively. The estimate of road salt application is within uncertainties of inventoried estimates of road salt loading and is 122 to 214% greater than recommended targets. Model predictions of chloride showed seasonal variation in chloride concentrations despite a large groundwater storage pool. Interannual variation of mean summer chloride concentration near the outlet varied up to 18%, and the total river length exceeding impairment thresholds varied 12%. Annual snowfall, which drives road salt loading, correlated with chloride impairment only in headwater streams, whereas concentration variability at the outlet was driven primarily by dilution from clean runoff-draining undeveloped forested areas of the watershed. The role of summer meteorology complicates the protection of freshwater systems from chloride contamination