The Land-Cover Cascade: Relationships Coupling Land and Water

Abstract

We introduce the land-cover cascade (LCC) as a conceptual framework to quantify the transfer of land-cover-disturbance effects to stream biota. We hypothesize that disturbance is propagated through multivariate systems through key variables that transform a disturbance and pass a reorganized disturbance effect to the next hierarchical level where the process repeats until ultimately affecting biota. We measured 31 hydrologic, geomorphic, erosional, and substrate variables and 26 biotic responses that have been associated with land-use disturbance in third- and fourth-order streams in the Blue Ridge physiographic province in western North Carolina (USA). Regression analyses reduced this set of variables to include only those that responded to land cover and/or affected biota. From this reduced variable set, hypotheses were generated that predicted the disturbance pathways affecting each biotic response following the land-cover-cascade design. Cascade pathways began with land cover and ended with biotic responses, passing through at least one intermediate ecosystem abiotic component. Cascade models were tested for predictive ability and goodness-of-fit using path analysis. Biota were influenced by near-stream urban, agricultural, and forest land cover as propagated by hydrologic (e.g., discharge), geomorphic (e.g., stream bank height), erosional (e.g., suspended sediments), and depositional streambed (e.g., substrate size) features occurring along LCC pathways, reflecting abiotic mechanisms mediating land-cover disturbance. Our results suggest that communities are influenced by land-cover change indirectly through a hierarchy of associated abiotic components that propagate disturbance to biota. More generally, the land-cover cascade concept and experimental framework demonstrate an organized approach to the generic study of cascades and the complex relationships between landscapes and streams.

Species traits reveal effects of land use, season and habitat on the potential subsidy of stream invertebrates to terrestrial food webs

“…Agricultural streams are often strongly modified relative to forested sites in the same region, reflecting both hydromorphological changes arising from losses of riparian vegetation, and direct anthropogenic modification of channel forms, e.g. dredging and agricultural channelization (Burcher et al 2007), with these impacts particularly prominent in our study region in central Sweden. These modifications often result in a stream profile characterised by long pool sequences separating short riffle sequences without meanders (Petersen 1992), in contrast with the more regular pool-riffle sequence which characterizes many more natural systems flowing through forest (Leopold et al 1964;Frainer et al 2014).…”

Artificial Aquatic Ecosystems

“…The condition of the watershed and landscape around any waterbody influences its condition [93], and artificial aquatic systems should be no different in this respect. Since humans tend to create artificial aquatic systems in and around heavily modified landscapes with substantial chemical inputs like agricultural fields, roads, and parking lots, artificial aquatic systems such as ditches tend to have lower water quality than their natural counterparts [94][95][96]. The communities of artificial aquatic systems also tend to reflect the local and regional species pools, yielding, for example, more exotic species in a restoration in a developed area [97].…”

Riverine Ecosystem Management

“…Up to now, it is a prime challenge to understand these functions in detail and to robustly manage riverine landscapes in a sustainable manner. Starting with the work of Hynes (1975), the scale of riverine management was understood to occur over entire river catchments or even river basins with several concepts that integrated this perception (Vannote et al 1980;Frissell et al 1986;Ward 1989;Fausch et al 2002;Ward et al 2002;Burcher et al 2007). These theoretical frameworks seek to understand and to quantify interactions between landscape conditions over large spatial extents and instream responses.…”

“…Hence, Wiens (2002) suggested to take the "land" out of landscape ecology to emphasize the importance of integrating landscape ecological approach into river research and to deepen the understanding on the interplay between terrestrial and aquatic ecosystems which should enable to perceive riverine ecosystems as "riverscapes" as proposed by Ward (1998). After Fausch et al (2002 and Wiens (2002), encouraging researchers and managers to consider the entire river environment, it was Burcher et al (2007) who introduced the land cover cascade concept in which disturbance stimuli are propagated through a series of hierarchical entities until they ultimately affect biota in their habitat. Subsequently, researchers expanded their thinking to integrate this "bigger picture" into pressure-impact analyses.…”