In-Stream Nitrogen Attenuation:  Model-Aggregation Effects and Implications for Coastal Nitrogen Impacts

Abstract

Eutrophication problems in coastal and marine waters worldwide emphasize the significance, for the scientific community as well as the whole society, of relevant quantification of catchment-scale nitrogen transport from land to coast. Different catchment-scale nitrogen budget models use, and base management recommendations on, quite different process representations of and spatial resolution approaches to in-stream nitrogen attenuation. We compare three different spatial resolution approaches to modeling nitrogen loss rates in streams of the same drainage basin. Results show that commonly used spatial model aggregation may lead to artificial decrease of calibrated nitrogen loss rates with increasing stream depth (or flow), in addition to any such dependences that may prevail in independently measurable reality. Coastal nitrogen impact predictions and practical management implications of large-scale model aggregation of nitrogen attenuation rates may further differ considerably from those based on rates from finer resolution modeling or independent measurements.

Effects of Inland Nitrogen Transport and Attenuation Modeling on Coastal Nitrogen Load Abatement

“…Such coarse catchment resolution does of course also influence optimal abatement solutions; however, in the direction of underestimating rather than overestimating the possible abatement inefficiency of coastal nitrogen load abatement that may result from oversimplified source-to-coast nitrogen transportattenuation modeling. This estimation error direction is indicated by the results of Darracq and Destouni (9), showing that higher spatial resolution in modeling of nitrogen transport-attenuation facilitates identification of greater possible efficiency gains by spatially nonuniform nitrogen abatement measures than lower spatial model resolution.…”

Quantification of advective solute travel times and mass transport through hydrological catchments

“…The advective travel time distributions that have been used in most previous studies have been approximated by assuming some common type of probability density function (e.g., log-normal, inverse Gaussian), which can be fully parameterized based on knowledge of only the possible mean and variance of solute travel times in the considered transport system. In this study, we adopt the Lagrangian advective travel time-based approach and extend it to quantify and investigate entire distributions of advective solute travel times in the two Swedish catchment cases and their different water subsystems, by the use of the flow and mass transport results that have already been modeled, tested against all available monitoring data and reported in a series of previous published studies of these catchment areas [19][20][21][22][23][24][25][26][27][28].…”

“…The travel time variability that exists at all scales in all catchments may to smaller or greater degree mask some important effects of these factors and mechanisms and lead to disparities between different solute transport models and results for different measurement and model scales [4,[18][19][20]. Such disparities limit our capability to incorporate field knowledge and to interpret and transfer results in and between different modeling frameworks and catchments.…”

“…In this paper, we investigate the possible quantification of solute travel time distributions in catchments, by the use of reported results on catchment-scale hydrological flow and mass transport modeling in two well-investigated, coastal Swedish catchments areas ( Fig. 1): the Norrström drainage basin [19][20][21][22][23][24] and the Forsmark catchment area [25][26][27][28]. In particular, we investigate here the role of different possible groundwater system representations for the quantification of solute travel times through catchments.…”

Water in Central Asia: an integrated assessment for science-based management

“…While some parts of Central Asia have experienced a recent depopulation, the region's overall population continues to grow. Improper municipal wastewater management in growing urban areas is another major pressure, leading to rising pollution levels in rivers and groundwater with regard to organic substances, nutrients and pathogens Darracq and Destouni 2005;Hofmann et al 2011;Malsy et al 2016), and posing sanitary risks for local settlers (Bosch et al 2007;Sorokovikova et al 2013;Uddin et al 2014). While in recent years, programs for the renewal of urban wastewater infrastructures have started in many parts of the region, decentral options still tend to be neglected, but would be viable solutions in regions with small settlements and low population densities (Khurelbaatar et al 2017).…”