Regression-based approaches are often employed to estimate riverine constituent concentrations and fluxes based on typically sparse concentration observations. One such approach is the recently developed WRTDS (“Weighted Regressions on Time, Discharge, and Season”) method, which has been shown to provide more accurate estimates than prior approaches in a wide range of applications.

Read more

Two statistical approaches, weighted regression on time, discharge, and season and generalized addi- tive models, have recently been used to evaluate water quality trends in estuaries. Both models have been used in similar contexts despite differences in statistical foundations and products. This study provided an empirical and qualitative comparison of both models using 29 years of data for two discrete time series of chlorophyll-a (chl-a) in the Patuxent River estuary.

Read more

The influence of sea level rise and warming on circulation and water quality of the Chesapeake Bay under projected climate conditions in 2050 were estimated by computer simulation. Four estuarine circulation scenarios in the estuary were run using the same watershed load in 1991-2000 period. They are, 1) the Base Scenario, which represents the current climate condition, 2) a Sea Level Rise Scenario, 3) a Warming Scenario, and 4) a combined Sea Level Rise and Warming Scenario.

Read more

Interactions among global change stressors and their effects at large scales are often proposed, but seldom evaluated. This situation is primarily due to lack of comprehensive, sufficiently long-term, and spatially extensive datasets. Seagrasses, which provide nursery habitat, improve water quality, and constitute a globally important carbon sink, are among the most vulnerable habitats on the planet.

Read more

Antimicrobial resistance is a global health issue. The discharge, maintenance and transfer of antimicrobial resistance to the aquatic environment and the risk this presents is relatively unknown. This work describes the presence and distribution of antimicrobial resistant Escherichia coli in surface waters of seven rivers in south east Queensland, Australia.

Read more

Derived from river monitoring data, concentration-discharge (C-Q) relationships are powerful indicators of export dynamics. Proper interpretation of such relationships can be made complex, however, if the ln(C)-ln(Q) relationships are nonlinear or if the relationships change over time, season, or discharge. Methods of addressing these issues by “binning” data can introduce artifacts that obscure underlying interactions among time, discharge, and season.

Read more

The export of nitrogen (N), phosphorus (P), and suspended sediment (SS) is a long-standing management con- cern for the Chesapeake Bay watershed, USA. Here we present a comprehensive evaluation of nutrient and sed- iment loads over the last three decades at multiple locations in the Susquehanna River basin (SRB), Chesapeake's largest tributary watershed.

Read more

A coupled estuarine hydrodynamic model and water quality model were used to analyze differences in destratification and anoxia/hypoxia reduction by wind directions in the north-south oriented Chesapeake estuary, USA. The predominant cross-channel bathymetry in the Bay's anoxic center is asymmetric with a steeper and narrower shoal on the eastern shore than on the western shore, which modifies wind-induced circulation differently for two opposite wind directions.

Read more

Ecological restoration of the Chesapeake through the Chesapeake Bay total maximum daily load (TMDL) requires the reduction of nitrogen, phosphorus, and sediment loads in the Chesapeake watershed because of the tidal water quality impairments and damage to living resources they cause. Within the Chesapeake watershed, the Conowingo Reservoir has been filling in with sediment for almost a century and is now in a state of near-full capacity called dynamic equilibrium.

Read more

Reduction of suspended sediment (SS), total phosphorus (TP), and total nitrogen is an important focus for Chesapeake Bay watershed management. The Susquehanna River, the bay’s largest tributary, has drawn attention because SS loads from behind Conowingo Dam (near the river’s mouth) have been rising dramatically. To better understand these changes, we evaluated histories of concentration and loading (1986−2013) using data from sites above and below Conowingo Reservoir.

Read more