Scale-dependent effects of land cover on water physico-chemistry and diatom-based metrics in a major river system, the Adour-Garonne basin (South Western France)

https://doi.org/10.1016/j.scitotenv.2013.06.107Get rights and content

Highlights

  • The spatial scale dependence of the “cascade effect” in a river system has been demonstrated.

  • The strength of the relationships between land cover and diatoms through water chemistry increases with the spatial scale.

  • The direct influence of land cover on diatoms metrics points out discontinuous processes.

  • The most detailed grain of land cover is the most relevant in the land-cover, water chemistry and diatoms relationships.

Abstract

The scale dependence of ecological phenomena remains a central issue in ecology. Particularly in aquatic ecology, the consideration of the accurate spatial scale in assessing the effects of landscape factors on stream condition is critical. In this context, our study aimed at assessing the relationships between multi-spatial scale land cover patterns and a variety of water quality and diatom metrics measured at the stream reach level. This investigation was conducted in a major European river system, the Adour-Garonne river basin, characterized by a wide range of ecological conditions. Redundancy analysis (RDA) and variance partitioning techniques were used to disentangle the different relationships between land cover, water-chemistry and diatom metrics.

Our results revealed a top-down “cascade effect” indirectly linking diatom metrics to land cover patterns through water physico-chemistry, which occurred at the largest spatial scales. In general, the strength of the relationships between land cover, physico-chemistry, and diatoms was shown to increase with the spatial scale, from the local to the basin scale, emphasizing the importance of continuous processes of accumulation throughout the river gradient. Unexpectedly, we established that the influence of land cover on the diatom metric was of primary importance both at the basin and local scale, as a result of discontinuous but not necessarily antagonist processes. The most detailed spatial grain of the Corine land cover classification appeared as the most relevant spatial grain to relate land cover to water chemistry and diatoms.

Our findings provide suitable information to improve the implementation of effective diatom-based monitoring programs, especially within the scope of the European Water Framework Directive.

Introduction

Understanding how ecological processes are interconnected over multiple spatial scales, from global patterns to local community structure, is of paramount importance for fundamental and applied research in ecology (Levin, 1992, Thompson et al., 2001). In freshwater ecosystems, key components of the ecosystem (e.g., climate, hydrology, land cover, water-chemistry or biology) are known to be hierarchically organized in space (Frissell et al., 1986, Allan et al., 1997, Heino, 2011). Such a spatial hierarchization may be perceived as an unforeseen chain of events made of unidirectional relationships between abiotic and biotic components, whose dynamic balance between the different components could be maintained by top-down or bottom-up “cascade effects”. In the scope of applied conservation, understanding at which scale the surrounding landscape and human disturbances may affect water quality at a given point is essential to adapt scale-appropriate strategies to protect and rehabilitate stream ecosystems (Gove et al., 2001). This is one of the major priorities of the European Water Framework Directive (WFD; 2000/60/EC European Parliament and Council, 2000) with the aim of maintaining and restoring the “good ecological status” of rivers by 2015.

While the hierarchical organization of freshwater ecosystems in space is widely recognized, very few studies have quantified the different relationships linking the key-components of the ecosystems over multiple spatial scales. Among these few studies, some have investigated the biological responses of freshwater communities to physical or chemical disturbances at single spatial scales (Roth et al., 1996, Strayer et al., 2003, Pan et al., 2004). Their results are usually not consensual and there is still debate regarding the predominant influence of local (e.g., Sponseller et al., 2001, Meador and Goldstein, 2003, Kail et al., 2009) versus large (e.g., Potapova and Charles, 2002, Park et al., 2006) spatial scale landscape factors on aquatic ecosystems. Another group of studies has examined the relationships between landscape metrics and a single key component of the hydrosystems, such as hydromorphological features (Orr et al., 2008, Buffagni et al., 2009), water physico-chemistry (Dodds and Oakes, 2006, Boeder and Chang, 2008) or biota (Hopkins and Burr, 2009, He et al., 2010).

In line with the WFD, the novelty of our research is to bridge the gap between previous studies by examining the relationships between land cover data and multiple ecosystem components (water physico-chemistry and benthic diatoms) at multiple spatial scales, from large (e.g. basin) to local (e.g., stream reach) scales, and combining them into a single analytical process. Our goal is to determine at which spatial scale land cover is likely to best explain local patterns of different water physico-chemical parameters and diatom metrics. The study was conducted in a major European river system, the Adour-Garonne basin (SW France), which hosts a diversity of ecological conditions, and is considered as a pilot study system in a number of European projects, such as Eurolimpacs (contract number 505540) and Biofresh (contract number 226874) of the 6th and 7th Framework Programmes.

The three main objectives were: 1) to assess the potential “cascade effect” from landscape factors to diatom metrics through water physico-chemistry; 2) to quantify the strength of the spatial scale dependencies between land cover, water physico-chemistry and diatom metrics; and 3) to discuss the relevance of the results in the light of the WFD to help implement effective diatom-based monitoring tools.

Section snippets

Study design and data collection

The Adour-Garonne hydrographic network (116,000 km2 with 120,000 km of watercourses) covers South West France and is composed of six main sub-basins. The river Garonne is the main channel, running over 580 km from the central Pyrenees in Spain, to the Gironde estuary on the Atlantic coast. For more details about the features of the Adour Garonne river networks see Park et al. (2006).

The study was designed to assess the strength of the relationship between different land cover spatial patterns, and

Results

The overall variance partitioning results for diatom and water chemistry RDA models are compiled in Table 2 and a summary is provided in Fig. 4. Overall, water chemistry models outperform diatom models in terms of goodness-of-fit, with adjusted-R2 values averaging 0.35 ± 0.10 and 0.28 ± 0.10, respectively (Fig. 4a). However both models show relatively similar spatial patterns. On the one hand, the standard deviation in the mean models goodness-of-fit between the three spatial grains (σ = 0.03) is

Cascade effect from land cover to diatom metrics through water chemistry

Our results provide evidence that, in the system we studied here, a top-down cascade effect relates land cover to diatom metrics through the indirect influence of water quality. The four statements tested to validate this cascade effect provide further understanding of the underlying processes involved. Firstly, the top-down effect is occurring at a large spatial extent only, in particular at the basin scale, while it is likely to be hidden by local conditions at smaller scales (ST 1 and 3).

Conclusion

By determining the spatial scale of land cover that best explains both the water physico-chemistry and the diatom metrics in a major river system, our study provides consistent answers to the three objectives presented in the Introduction.

Our results provide evidence of a cascade effect occurring at a large spatial scale over the study region, linking diatom metrics to land cover patterns indirectly through water physico-chemistry. Since the cascade effect was not shown to occur at small

Acknowledgments

This research, supported by the Eurolimpacs (GOCE-CT-2003-505540) and Biofresh (FP7-ENV-2008-226874) 6th and 7th Framework European projects, was performed in the “Evolution & Diversité Biologique” laboratory, part of the “Laboratoire d'Excellence” (LABEX) entitled TULIP (ANR-10-LABX-41). We also thank John Woodley and Cândida Shinn for their precious English corrections, and the anonymous referees for their constructive comments.

References (66)

  • N.J. Smucker et al.

    Spatial factors contribute to benthic diatom structure in streams across spatial scales: considerations for biomonitoring

    Ecol Indic

    (2011)
  • J. Tison et al.

    Typology of diatom communities and the influence of hydro-ecoregions: a study on the French hydrosystem scale

    Water Res

    (2005)
  • J. Tison et al.

    Predicting diatom reference communities at the French hydrosystem scale: a first step towards the definition of the good ecological status

    Ecol Model

    (2007)
  • G. Urrea et al.

    Epilithic diatom assemblages and their relationship to environmental characteristics in an agricultural watershed (Guadiana River, SW Spain)

    Ecol Indic

    (2009)
  • AFNOR NF EN 13946

    Water quality

    Guidance standard for the routine sampling and pretreatment of benthic diatoms from rivers

    (2003)
  • J.A. Aitkenhead et al.

    The relationship between dissolved organic carbon in stream water and soil organic carbon pools at different spatial scales

    Hydrol Process

    (1999)
  • J.D. Allan

    Landscape and riverscapes: the influence of land use on stream ecosystems

    Annu Rev Ecol Evol Syst

    (2004)
  • J.D. Allan et al.

    The influence of catchment land use on stream integrity across multiple spatial scales

    Freshw Biol

    (1997)
  • F. Bernard Daniel et al.

    Influences of spatial scale and soil permeability on relationships between land cover and baseflow stream nutrient concentrations

    Environ Manage

    (2010)
  • A. Buffagni et al.

    Hydromorphology and land use at different spatial scales: expectations in a changing climate scenario for medium-sized rivers of the Western Italian Alps

    Fundam Appl Limnol

    (2009)
  • Cemagref

    Etude des méthodes biologiques quantitatives d'appréciation de la qualité des eaux

  • M.W. Diebel et al.

    Landscape planning for agricultural non-point source pollution reduction I: a geographical allocation framework

    Environ Manage

    (2008)
  • W.K. Dodds et al.

    Controls on nutrients across a prairie stream watershed: land use and riparian cover effects

    Environ Manage

    (2006)
  • European Environment Agency

    CORINE Land Cover Project

    (2005)
  • European Parliament and Council

    Water Framework Directive 2000/60/EC establishing a framework for community action in the field of water policy

    Off J Eur Communities

    (2000)
  • C.A. Frissell et al.

    A hierarchical framework for stream habitat classification: viewing streams in a watershed context

    Environ Manage

    (1986)
  • R.M. Goldstein et al.

    Can basin land use effects on physical characteristics of streams be determined at broad geographic scale?

    Environ Monit Assess

    (2007)
  • N.E. Gove et al.

    Effects of scale on land use and water quality relationships: a longitudinal basin wide perspective

    J Am Water Res Assoc

    (2001)
  • M.B. Griffith et al.

    Multivariate analysis of periphyton assemblages in relation to environmental gradients in Colorado rocky mountain streams

    J Phycol

    (2002)
  • J. Heino

    A macroecological perspective of diversity patterns in the freshwater realm

    Freshw Biol

    (2011)
  • A.T. Herlihy et al.

    The relationships between stream chemistry and watershed land cover data in the Mid-Atlantic Region, U.S.

    Water Air Soil Pollut

    (1998)
  • L.B. Johnson et al.

    Landscape influences on water chemistry in Midwestern stream ecosystems

    Freshw Biol

    (1997)
  • J. Kail et al.

    Relation between floodplain land use and river hydromorphology on different spatial scales — a case study from two lower-mountain catchments in Germany

    Fundam Appl Limnol

    (2009)
  • Cited by (0)

    View full text