Societal, land cover and climatic controls on river nutrient flows into the Baltic Sea

Study region River basins draining into the Baltic Sea, known as the Baltic Sea Drainage Basin (BSDB). Study focus Dramatic shifts in water quality have been observed in the Baltic Sea in past decades. This study investigated the spatial distribution of trends in nitrogen (N) and phosphorus (P) in relation to societal, land cover and climatic changes. A 31-year record of observed catchment scale nutrient concentration and discharge data for the period 1970–2000 was combined with climate and land cover data. A Mann–Kendall test was applied to reveal trends in N and P, the N:P ratio, discharge, temperature and precipitation. Classical factor analysis and Kendall's rank correlation identified the most important relationships between nutrients, land cover and climate. New hydrological insights for the region A large spatial variability in N and P trends was observed with a notable difference between the east and west of the BSDB. The existence of regional trend variations are important for nutrient load reduction management strategies. Specifically, it is recommended that strategies targeting seawater eutrophication should focus more on P rather than N reduction because increasing P in the eastern catchments is responsible for the overall declining trend in the N:P ratio, an important trigger for algal blooms

Unsupervised classification of saturated areas using a time series of remotely sensed images

The spatial distribution of saturated areas is an important consideration in numerous applications, such as water resource planning or siting of management practices. However, in humid well vegetated climates where runoff is produced by saturation excess processes on hydrologically active areas (HAA) the delineation of these areas can be difficult and time consuming. A technique that can simply and reliably predict these areas would be a powerful tool for scientists and watershed managers tasked with implementing practices to improve water quality. Remotely sensed data is a source of spatial information and could be used to identify HAAs. This study describes a methodology to determine the spatial variability of saturated areas using a temporal sequence of remotely sensed images. The Normalized Difference Water Index (NDWI) was derived from medium resolution Landsat 7 ETM+ imagery collected over seven months in the Town Brook watershed in the Catskill Mountains of New York State and used to characterize the areas susceptible to saturation. We found that within a single land cover, saturated areas were characterized by the soil surface water content when the vegetation was dormant and leaf water content of the vegetation during the growing season. The resulting HAA map agreed well with both observed and spatially distributed computer simulated saturated areas (accuracies from 49 to 79). This methodology shows that remote sensing can be used to capture temporal variations in vegetation phenology as well as spatial/temporal variation in surface water content, and appears promising for delineating saturated areas in the landscape

Seasonal flows of international British Columbia-Alaska rivers: The nonlinear influence of ocean-atmosphere circulation patterns

The northern portion of the Pacific coastal temperate rainforest (PCTR) is one of the least anthropogenically modified regions on earth and remains in many respects a frontier area to science. Rivers crossing the northern PCTR, which is also an international boundary region between British Columbia, Canada and Alaska, USA, deliver large freshwater and biogeochemical fluxes to the Gulf of Alaska and establish linkages between coastal and continental ecosystems. We evaluate interannual flow variability in three transboundary PCTR watersheds in response to El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO), and North Pacific Gyre Oscillation (NPGO). Historical hydroclimatic datasets from both Canada and the USA are analyzed using an up-to-date methodological suite accommodating both seasonally transient and highly nonlinear teleconnections. We find that streamflow teleconnections occur over particular seasonal windows reflecting the intersection of specific atmospheric and terrestrial hydrologic processes. The strongest signal is a snowmelt-driven flow timing shift resulting from ENSO- and PDO-associated temperature anomalies. Autumn rainfall runoff is also modulated by these climate modes, and a glacier-mediated teleconnection contributes to a late-summer ENSO-flow association. Teleconnections between AO and freshet flows reflect corresponding temperature and precipitation anomalies. A coherent NPGO signal is not clearly evident in streamflow. Linear and monotonically nonlinear teleconnections were widely identified, with less evidence for the parabolic effects that can play an important role elsewhere. The streamflow teleconnections did not vary greatly between hydrometric stations, presumably reflecting broad similarities in watershed characteristics. These results establish a regional foundation for both transboundary water management and studies of long-term hydroclimatic and environmental change

Modeling the release of Escherichia coli from soil into overland flow under raindrop impact

Pathogen transport through the environment is complicated, involving a variety of physical, chemical, and biological processes. This study considered the transfer of microorganisms from soil into overland flow under rain-splash conditions. Although microorganisms are colloidal particles, they are commonly quantified as colony-forming units (CFUs) per volume rather than as a mass or number of particles per volume, which poses a modeling challenge. However, for very small particles that essentially remain suspended after being ejected into ponded water and for which diffusion can be neglected, the Gao model, originally derived for solute transfer from soil, describes particle transfer into suspension and is identical to the Hairsine–Rose particle erosion model for this special application. Small-scale rainfall experiments were conducted in which an Escherichia coli (E. coli) suspension was mixed with a simple soil (9:1 sand-to-clay mass ratio). The model fit the experimental E. coli data. Although re-conceptualizing the Gao solute model as a particle suspension model was convenient for accommodating the unfortunate units of CFU ml−1, the Hairsine–Rose model is insensitive to assumptions about E. coli per CFU as long as the assumed initial mass concentration of E. coli is very small compared to that of the soil particle classes. Although they undoubtedly actively interact with their environment, this study shows that transport of microorganisms from soil into overland storm flows can be reasonably modeled using the same principles that have been applied to small mineral particles in previous studies