Quantifying relationships between land‐use gradients and structural and functional indicators of stream ecological integrity

Abstract

1. Modification of natural landscapes and land-use intensification are global phenomena that can result in a range of differing pressures on lotic ecosystems. We analysed national-scale databases to quantify the relationship between three land uses (indigenous vegetation, urbanisation and agriculture) and indicators of stream ecological integrity. Boosted regression tree modelling was used to test the response of 14 indicators belonging to four groups -water quality (at 578 sites), benthic invertebrates (at 2666 sites), fish (at 6858 sites) and ecosystem processes (at 156 sites). Our aims were to characterise the ecological response curves of selected functional and structural metrics in relation to three land uses, examine the environmental moderators of these relationships and quantify the relative utility of metrics as indicators of stream ecological integrity. 2. The strongest indicators of land-use effects were nitrate + nitrite, delta-15 nitrogen value (d 15 N) of primary consumers and the Macroinvertebrate Community Index (a biotic index of organic pollution), while the weakest overall indicators were gross primary productivity, benthic invertebrate richness and fish richness. All indicators declined in response to removal of indigenous vegetation and urbanisation, while variable responses to agricultural intensity were observed for some indicators. 3. The response curves for several indicators suggested distinct thresholds in response to urbanisation and agriculture, specifically at 10% impervious cover and at 0.1 g m )3 nitrogen concentration, respectively. 4. Water quality and ecosystem process indicators were influenced by a combination of temperature, slope and flow variables, whereas for macroinvertebrate indicators, catchment rainfall, segment slope and temperature were significant environmental predictor variables. Downstream variables (e.g. distance to the coast) were significant in explaining residual variation in fish indicators, not surprisingly given the preponderance of diadromous fish species in New Zealand waterways. The inclusion of continuous environmental variables used to develop a stream typology improved model performance more than the inclusion of stream type alone. 5. Our results reaffirm the importance of accounting for underlying spatial variation in the environment when quantifying relationships between land use and the ecological integrity of streams. Of distinctive interest, however, were the contrasting and complementary responses of different indicators of stream integrity to land use, suggesting that multiple indicators are required

Community–environment relationships of riverine invertebrate communities in central Chinese streams

“…Kail et al (2012) found thresholds of 16.3 % urban landuse in german catchments limiting ecological quality at the sites, Collier et al (2013) linked less than 20 % natural vegetation cover to changes in ecosystems functions and Death and Collier (2010) related the amount of catchment natural vegetation to water quality or biodiversity. However, in terms of biotic influences, land use can alter community composition and biodiversity patterns (Allan 2004;Harding et al 1998) and functional indices (Clapcott et al 2012;Collier et al 2013), but despite altering composition, this may not influence other environmental linkages including those between productivity, disturbance and diversity (Tonkin and Death 2012).…”

A multimetric approach for predicting the ecological integrity of New Zealand streams

“…We analysed metrics calculated using a range of regional and national datasets as described in Clapcott et al (2012). Metrics included water quality metrics (water visual clarity -Clarity, nitrate-N and nitrite-N concentration -NOx), macroinvertebrate metrics (Macroinvertebrate Community Index -MCI (average sensitivity score per taxon (Stark, 1985)), number of species producing once in a life cycle -Cycle), fish metrics (index of biological integrity -F-IBI (Joy and Death, 2004), percent of native fish species -Native) and ecosystem process metrics (ecosystem respiration -ER, gross primary production -GPP, cellulose decomposition potential -Cotton, δ 15 N of primary consumers -D15N).…”

“…measures that have been and can be widely adopted and communicated). We used a boosted regression tree (BRT) approach (Elith et al, 2008), to model the response of candidate metrics to land use and environmental gradients at a national scale as described in Clapcott et al (2011). A two-step model was developed where in the first step we examined the metric response to three land-use gradients: percentage of native vegetation cover remaining (VegR), percentage of impervious cover (IC), and the log-transformed predicted stream N concentration (LogN; based on landuse intensity whereby estimated nitrogen load is standardised by stream flow (Woods et al, 2006)).…”

“…Model validation showed that this two-step approach had improved predictive accuracy compared to a simple "all-in" model, we suspect due to the fixed partitioning of variance to land-use effects. To predict "expected" reference values, first we calculated the average metric value at sites with >95% native vegetation cover and 0% urban cover (N ranged from 5−40 and represented approximately 10% of our training data with good geographical representation, Clapcott et al, 2011). We then used the fitted functions from the second step to estimate how these reference values will vary spatially on a national scale due to environmental variability in the absence of land-use effects.…”

“…For example, in a parallel investigation of fish, macroinvertebrates and diatom assemblages, Carlisle et al (2008) showed how a single group evaluation indicated impaired conditions on average much less often than when several groups were used. Similarly, a recent New Zealand study illustrated how different water quality, macroinvertebrate and fish indicators varied in their responses to land-use stressors (Clapcott et al, 2012). Comparable studies suggest that the assessment of multiple groups of organisms has the potential to provide a more robust evaluation of ecological integrity than the assessment of a single group (Brown et al, 2009;Waite, 2014).…”