Document Type

Dissertation - Open Access

Award Date

2017

Degree Name

Doctor of Philosophy (PhD)

Department / School

Natural Resource Management

First Advisor

Katie N. Bertrand

Keywords

fish, fragmentation, stream conservation, tagging

Abstract

Landscape homogenization and the degradation of riparian areas has greatly impaired stream ecosystems throughout North America. Conservation programs may repair riparian ecosystems to indirectly improve water quality and instream habitat heterogeneity in hopes to elicit biological responses. However, focused manipulations on isolated stream fragments have rarely achieved biological goals. Prairie streams with restored riparian areas were appraised (chemical, physical, and biological variables) to quantify the indirect effects of prevalent grassland conservation practices on aquatic resources. Riparian rehabilitation, via passive methods, promoted bank-stabilizing vegetation along all conservation stream reaches. Riparian vegetation and function quickly recovered from previous agricultural disturbances at conservation reaches. Substantial animal trampling and grazing pressure persisted at reference sites and restricted vegetation growth. Grassland conservation actions improved water quality and restored processes that create diverse instream habitat complexes in adjacent streams. Despite dramatic changes to riparian areas and subsequent improvements to instream environments, benthic invertebrate and fish assemblages have yet to respond to conservation. Restoration efforts that assume that ‘if you (re-)build it, they will come’ (‘field of dreams’ hypothesis), may underestimate the many other barriers to the restoration of biotic diversity. Restored stream reaches were not created equally and each have different colonization prospects when environmental pressures were removed. By considering the local effects of riparian restoration and the riverscape properties that dictate biotic responses, I was better able to explain conservation outcomes. I evaluated three alternative hypotheses to explain the limited biotic response to restoration efforts: (1) connections to newly available habitats remained severed; (2) regional assemblages lack species adapted to utilize opened niches; and (3) the niche space created did not benefit local species. The fragmentation of stream networks has severed historic movement pathways and potentially limited opportunities for fish to colonize restored stream reaches. To describe the relative likelihood that prairie fishes bypass anthropogenic barriers I quantified their swimming and jumping abilities. Stream fishes are not equally vulnerable to instream barriers, but all failed to circumvent relatively minor obstacles. Small vertical barriers (> 5 cm) blocked most fish passage and, with access, all species were unable to traverse relatively short obstacles with moderate water velocities. Abundant barriers to recolonization and limited tools to improve passage for small-bodied prairie fishes will restrict colonization of nearby habitats when they are improved. Interpreting biological responses requires consideration of the regional species pools from which restored reaches would recruit individuals. Conservation efforts in watersheds with small, impoverished species pools are unlikely to elicit a measurable response from aquatic assemblages. By considering the regional species pool, I identified many areas with few aquatic taxa available for colonization. Future colonization by many aquatic taxa is unlikely at a large number conservation sites throughout the James River basin. The determination of specific environmental targets for stream restoration efforts to benefit particular taxa and biotic diversity is critical but often addressed with limited data. My results suggest that benthic invertebrates and fishes strongly respond to changes to the riparian area that increase ground vegetation and tree cover. Fish and benthic invertebrate diversity was highest when instream cover (woody debris and overhanging vegetation) was available in areas with large substrates and abundant aquatic plants. Grassland conservation efforts created niche space that is beneficial to local aquatic fauna and rare in degraded reaches, but that are not utilized in inaccessible areas. Managers can supplement riparian rehabilitation efforts by providing large substrates and woody debris in areas with abundant aquatic and overhanging vegetation. Although the cumulative protected area exceeds 81,000 acres, each conservation easement only represents a sliver of the riverscape. Grassland conservation improved water quality and indirectly created heterogeneous stream habitats, but not all restored stream reaches were created equally. Stream fragmentation and ongoing, degenerative land practices may outdo the positive effects of restoring minority fractions of watersheds. The development of niche space didn’t directly translate to successful colonization and occupation by aquatic life. Strategic investments in species rich areas with few instream barriers are most likely to achieve aquatic diversity goals.

Library of Congress Subject Headings

Aquatic organisms -- Effect of habitat modification on.
Grassland restoration.
Stream restoration.
Fragmented landscapes.

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

143

Publisher

South Dakota State University

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Rights Statement

In Copyright