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Arable land use is generally assumed to be the largest contributor to agricultural diffuse pollution. This study adds to the growing evidence that conventional temperate intensively managed lowland grasslands contribute significantly to soil erosion and diffuse pollution rates. This is the first grassland study to monitor hydrological characteristics and multiple pollutant fluxes (suspended sediment [SS] and the macronutrients: total oxidized nitrogen-N [TONN], total phosphorus [TP], and total carbon [TC]) at high temporal resolution (monitoring up to every 15 min) over 1 yr. Monitoring was conducted across three fields (6.5-7.5 ha-1) on the North Wyke Farm Platform, UK. The estimated annual erosion rates (up to 527.4 kg ha-1), TP losses (up to 0.9 kg ha-1), and TC losses (up to 179 kg ha-1) were similar to or exceeded the losses reported for other grassland, mixed land-use, and arable sites. Annual yields of TONN (up to 3 kg ha-1) were less than arable land-use fluxes and earlier grassland N studies, an important result as the study site is situated within a Nitrate Vulnerable Zone. The high-resolution monitoring allowed detailed "system's functioning" understanding of hydrological processes, mobilization-transport pathways of individual pollutants, and the changes of the relative importance of diffuse pollutants through flow conditions and time. Suspended sediment and TP concentrations frequently exceeded water quality guidelines recommended by the European Freshwater Fisheries Directive (25 mg L-1) and the European Water Framework Directive (0.04 mg soluble reactive P L-1), suggesting that intensively managed grasslands pose a significant threat to receiving surface waters. Such sediment and nutrient losses from intensively managed grasslands should be acknowledged in land management guidelines and advice for future compliance with surface water quality standards. [ABSTRACT FROM AUTHOR]

During the last 150 years, land degradation across the semi-arid grasslands of the south-western United States has been associated with an increase in runoff and erosion. Concurrent with this increase in runoff and erosion is a loss of nitrogen (N) and phosphorus (P), which are plant-essential nutrients. This study investigates the runoff-driven redistribution and loss of dissolved and particulate-bound N and P that occurs during natural runoff events over a trajectory of degradation, from grassland to degraded shrubland, in central New Mexico. Runoff-driven nutrient dynamics were monitored at four stages over a transition from grassland to shrubland, for naturally occurring rainfall events over 10 × 30 m bounded runoff plots. Results show that particulate-bound forms of N and P are responsible for most of N and P lost from the plots due to erosion occurring during runoff events. Results suggest that for high-magnitude rainfall events, the output of N and P from the plots may greatly exceed the amount input into the plots, particularly over shrub-dominated plots where erosion rates are higher. As these results only become apparent when monitoring these processes over larger hillslope plots, it is important to recognize that processes of nutrient cycling related to the islands of fertility hypothesis may have previously been overstated when observed only at smaller spatial scales. Thus, the progressive degradation of semi-arid grassland ecosystems across the south-western United States and other semi-arid ecosystems worldwide has the potential to affect N and P cycling significantly through an increase in nutrient redistribution and loss in runoff. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents a study which evaluates the MAHLERAN model, which is a numerical model for assessing hillslope-landscape erosion, runoff and nutrients. A sensitivity analysis shows that the numerical model is consistent with analytical model of Parson and colleagues (2004), and demonstrates that down slope patterns of sediment flux on hillslope are complex interaction of rainfall intensity, duration and pattern, hillslope gradient, surface roughness and sediment size. The model is also capable of reproducing the sedigraph with an overall normalized root-mean-square error of 18.4% and Nash-Sutcliffe efficiency of 0.90.

The article presents a Model for Assessing Hillslope-Landscape Erosion, Runoff And Nutrients (MAHLERAN), which is used to scale erosion rates. It is stated that this model is based on particle-travel distance that overcomes existing limitations by integrating parameterizations of the different detachment and transport mechanisms that take place in water erosion in hillslopes and small catchments. Moreover, it is said that this approach assumes that sediment is transported through the system in suspension.

The article presents a discussion concerning the misrepresentation of the USLE concerning sediment delivery. It has been noted by the author that the assertion that the application of the USLE to predicting soil losses within a catchment or watershed is not sound because the USLE provides an estimate of erosion that would be measured if the entire area were divided up into 22.1 meter long plots. In addition, the slope length factor was derived from data obtained using a wide range of plot lengths.

Despite the wealth of soil erosion models available for the prediction of both runoff and soil loss at a variety of scales, little quantification is made of uncertainty and error associated with model output. This in part reflects the need to produce unequivocal or optimal results for the end user, which will often be an unrealistic goal. This paper presents a conceptually simple methodology, Generalized Likelihood Uncertainty Estimation (GLUE), for assessing the degree of uncertainty surrounding output from a physically based soil erosion model, the Water Erosion Prediction Project (WEPP). The ability not only to be explicit about model error but also to evaluate future improvements in parameter estimation, observed data or scientific understanding is demonstrated. This approach is applied to two sets of soil loss/runoff plot replicates, one in the UK and one in the USA. Although itis demonstrated that observations can be largely captured within uncertainty bounds, results indicate that these uncertainty bounds are often wide, reflecting the need to qualify results that derive from optimum parameter sets, and to accept the concept of equifinality within soil erosion models. Attention is brought to the problem of under-prediction of large events/over-prediction of small events, as an areawhere model improvements could be made, specifically in the case of relatively dry years. Finally it is proposed that such a technique ofmodel evaluation be employed more widely within the discipline so asto aid the interpretation and understanding of complex model output. [ABSTRACT FROM AUTHOR]

Summary: Land degradation in arid and semi-arid areas, as a consequence of the invasion of grasslands by shrubs, is often associated with an increase in runoff and erosion and a change in nutrient transport. Modelling of nutrient transport during runoff events (in particular particulate-bound nutrients), is especially important, since the spatial redistribution of nutrients (in addition to water and sediment) can have significant implications for vegetation dynamics in these ecosystems. In this study, Mahleran (Model for Assessing Hillslope to Landscape Erosion Runoff, And Nutrients) is extensively evaluated against runoff and erosion data from four plots (representative of different stages of land degradation) over a transition from grassland to shrubland, at the Sevilleta National Wildlife Refuge in New Mexico, USA. A new particulate-bound nutrient module was developed to include a representation of particulate-bound nutrient dynamics, which is an important form of nutrient transport in these ecosystems. Understanding dynamics of both dissolved and particulate-bound nutrient dynamics during runoff events is imperative, because of their differing roles in terms of nutrient bioavailability and potential implications for plant dynamics. Results of the model evaluation show that the runoff and erosion components of Mahleran perform reasonably well, as does the new particulate-bound nutrient sub-model, though not consistently. Performance of the particulate-bound nutrient model was better for the end-member plots, because of better parameterization data available for end-member vegetation types. Since the particulate-bound nutrient sub-model is by necessity strongly dependent on the simulated erosion rate, the performance of the particulate-bound nutrient model is dependent on the performance of the erosion component of Mahleran, so that when erosion is well represented by the model, so typically are particulate nutrient transfers. The performance of the dissolved nutrient component of Mahleran was poor in this application, which indicates that the process representation for this semi-arid environment and the parameterisation of the dissolved nutrient component were inadequate. Results from the model evaluation suggest that an improved understanding of dissolved nutrient dynamics during runoff events and simulation if inter-event nutrient dynamics is required, in order to improve the level of process representation within modelling approaches and thus the ability to simulate dissolved nutrient dynamics and their subsequent effects on other ecosystem processes. [Copyright &y& Elsevier]

Abstract: Connectivity as a concept has been increasingly part of discussions or explanations in hydrology, geomorphology and ecology. We address recent critiques of this approach by demonstrating how a refinement which distinguishes structural connectivity from functional connectivity can be used to explain patterns observed in very different environmental systems. These systems are found in linkages between surface and subsurface flowpaths and the hyporheos in the River Don, a temperate river channel in Yorkshire, UK; in surface and subsurface fluxes in agricultural land in the UK; and in vegetation and surface conditions in a degrading environment at the Sevilleta LTER site in the semi-arid Southwest USA. First, we demonstrate long-term geological and structural controls mediated by in-channel processes. Second, human organization of landscape elements is a significant control on runoff and erosion, so that similar events can produce very different responses (and vice versa). Third, linkages between the removal of grass vegetation and runoff and erosion produce non-linear and path-dependent feedbacks which control the subsequent degradation of the landscape, making the process difficult to reverse. As a result of these studies, we argue that even in cases where connectivity cannot be directly quantified (at least at present), this limitation does not prevent the concept from being a useful heuristic device for exploring responses of complex systems. Furthermore, this result implies that an increasing need exists for disciplinary connectivity to investigate such systems. [Copyright &y& Elsevier]

• Open-access geodatabase and web-map has been created for soil erosion community. • Of the records held within the geodatabase (1566) 41.5% report presence of erosion. • Median erosion rate on arable land was 0 t ha−1 yr−1, maximum was 91.7 t ha−1 yr−1. • Existing data do not describe national-scale soil erosion rates due to biases in data. • Criteria presented for future replicable, comparable and robust studies. Accelerated soil erosion can result in substantial declines in soil fertility and has devastating environmental impacts. Consequently, understanding if rates of soil erosion are acceptable is of local and global importance. Herein we use empirical soil erosion observations collated into an open access geodatabase to identify the extent to which existing data and methodological approaches can be used to develop an empirically-derived understanding of soil erosion in the UK (by way of an example). The findings indicate that whilst mean erosion rates in the UK are low, relative to the rest of Europe for example, 16% of observations on arable land were greater than the supposedly tolerable rate of 1 t ha−1 yr−1 and maximum erosion rates were as high as 91.7 t ha−1 yr−1. However, the analysis highlights a skew in existing studies towards locations with a known erosion likelihood and methods that are biased towards single erosion pathways, rather than an all-inclusive study of erosion rates and processes. Accordingly, we suggest that future soil erosion research and policy must address these issues if an accurate assessment of soil erosion rates at the national-scale are to be established. The interactive geodatabase published alongside this paper offers a platform for the simultaneous development of soil erosion research, formulation of effective policy and better protection of soil resources. [ABSTRACT FROM AUTHOR]