Identifying the spatial scale of land use that most strongly influences overall river ecosystem health score

Abstract

Catchment and riparian degradation has resulted in declining ecosystem health of streams worldwide. With restoration a priority in many regions, there is an increasing interest in the scale at which land use influences stream ecosystem health. Our goal was to use a substantial data set collected as part of a monitoring program (the Southeast Queensland, Australia, Ecological Health Monitoring Program data set, collected at 116 sites over six years) to identify the spatial scale of land use, or the combination of spatial scales, that most strongly influences overall ecosystem health. In addition, we aimed to determine whether the most influential scale differed for different aspects of ecosystem health. We used linear-mixed models and a Bayesian model-averaging approach to generate models for the overall aggregated ecosystem health score and for each of the five component indicators (fish, macroinvertebrates, water quality, nutrients, and ecosystem processes) that make up the score. Dense forest close to the survey site, mid-dense forest in the hydrologically active near-stream areas of the catchment, urbanization in the riparian buffer, and tree cover at the reach scale were all significant in explaining ecosystem health, suggesting an overriding influence of forest cover, particularly close to the stream. Season and antecedent rainfall were also important explanatory variables, with some land-use variables showing significant seasonal interactions. There were also differential influences of land use for each of the component indicators. Our approach is useful given that restoring general ecosystem health is the focus of many stream restoration projects; it allowed us to predict the scale and catchment position of restoration that would result in the greatest improvement of ecosystem health in the regions streams and rivers. The models we generated suggested that good ecosystem health can be maintained in catchments where 80% of hydrologically active areas in close proximity to the stream have mid-dense forest cover and moderate health can be obtained with 60% cover.

Science to Support Management of Receiving Waters in an Event-Driven Ecosystem: From Land to River to Sea

“…Variation due to land use changes (e.g., loss of riparian forest cover) was therefore explicitly accounted for beyond that due to natural variation. The study found that 60%-80% upstream riparian cover of mid-dense forest would be required to maintain acceptable river health outcomes for the region (see also Section 4), including diverse communities of macroinvertebrate and native fish species [19]. Overall forest cover in the catchments was also found to have a significant effect on river health, as measured by the water quality and nutrient indicators.…”

“…Contrary to common belief, much of the phosphorus running off the catchment is in the dissolved inorganic form or loosely bound to soils owing to release from soil during wetting events [28][29][30]. As a result, the phosphorus can directly stimulate phytoplankton blooms, although the spatial and temporal scales over which this occurs depends on the turbidity of inflowing waters (which alters light availability) and the size, timing and source of those waters [19].…”

“…An analysis of the first six years of freshwater EHMP data indicates that reduction in riparian cover in particular is associated with a reduction in river health, and is an important driver of declining water quality and freshwater diversity across the region [19]. Variation in river health due to natural versus anthropogenic effects was determined using mixed models that included variables describing variation in rainfall across sites during the sampling period, variables for seasonality, spatially-explicit land use variables, and a random component to capture natural variation among sites.…”

“…Reducing loads of nutrients and sediment from catchments; Revegetating riparian zones and catchments [19,68] Macroinvertebrate and native fish diversity decline…”

Spatial patterns of water quality in Xingu River Basin (Amazonia) prior to the Belo Monte dam impoundment

“…Conditions of topography and land use are also important factors that influence the water quality in lotic environments (Sheldon et al, 2012), requiring the use of methods of study that focus both the ecological and anthropogenic processes occurring in the landscape scale and/or in the watershed as a whole (Likens, 1984;Wiens, 1989;Zalewski, 2000;Turner et al, 2001;Tundisi et al, 2008).…”