Effects of Timber Harvest on River Food Webs: Physical, Chemical and Biological Responses

J Timothy Wootton,Tamara Natasha Romanuk

doi:10.1371/journal.pone.0043561

Abstract

I compared physical, chemical and biological characteristics of nine rivers running through three timber harvest regimes to investigate the effects of land use on river ecosystems, to determine whether these corresponded to changes linked with downstream location, and to compare the response of different types of indicator variables. Physical variables changed with downstream location, but varied little with timber harvest. Most chemical variables increased strongly with timber harvest, but not with downstream location. Most biological variables did not vary systematically with either timber harvst or downstream location. Dissolved organic carbon did not vary with timber harvest or downstream location, but correlated positively with salmonid abundance. Nutrient manipulations revealed no general pattern of nutrient limitation with timber harvest or downstream location. The results suggest that chemical variables most reliably indicate timber harvest impact in these systems. The biological variables most relevant to human stakeholders were surprisingly insensitive to timber harvest, however, apparently because of decoupling from nutrient responses and unexpectedly weak responses by physical variables.

Highlights

Determining the effects of human activities such as land use on ecosystems is important for shaping management strategies and can provide insight into the structure and function of ecosystems
Physical Variables Physical conditions generally tended to vary with downstream location, but were inconsistently related to timber harvest (Fig. 2, Table 1)
Physical variables measured in this study generally varied with downstream location as previously expected [19], with canopy cover generally declining, and water temperature,and river width increasing with downstream location in a river

Summary

Introduction

Determining the effects of human activities such as land use on ecosystems is important for shaping management strategies and can provide insight into the structure and function of ecosystems. The effects of human activity on river systems is often of particular interest because such activity can directly impact rivers through such mechanisms as water extraction, changes in flow regime and channel morphology, discharge of wastes, and changes in direct insolation. It can indirectly impact rivers because of water flow through the surrounding watershed. Taking a more holistic view of river response to human activity may increase our understanding of the mechanisms of impact, which in turn may change our perspective on appropriate management strategies to take [e.g. 13,14]

Objectives

Methods

Results

Conclusion