Mitigating the impacts of stream and lake regulation in the flathead river catchment, Montana, USA: An ecosystem perspective

Abstract

ABSTRACT1. Seventy-two per cent of the Flathead River catchment (22 241 km2) is federally designated and protected as wilderness or national park. Thus, the catchment remains one of the more pristine areas of its size in the temperate latitudes of the world.2. Discharge in the downstream reaches of the river system outside the protected areas is regulated by three dams for flood control and hydropower production. These dams have blocked natural migration of native fish from Flathead Lake (496 km') and isolated populations in sub-catchments. Temperature and erratic flow fluctuations have altered phenologies of river zoobenthos and fish, and in dam tailwaters aquatic biodiversity is drastically reduced in comparison to unregulated segments.3. Ecological problems caused by changing water quality conditions, altered land-use patterns and introductions of non-native biota are interactive with the impacts of stream and lake level regulation, thereby emphasizing the complexity of this river-lake ecosystem.4. Mitigation of the effects of regulation is compromised by differing management priorities and regulatory mandates of County, State, Tribal, and Federal agencies responsible for natural resource management within the catchment. Moreover, economic and ecological interests outside the Flathead influence the way flows are regulated within the catchment.5. The most pervasive influences of stream and lake regulation can be ameliorated by retrofitting the hypolimnial release dam with a selective depth outlet structure to allow temperature control, and by controlling changes in flow rates to create a more natural hydrograph in the tailwaters of the large dams. Allowing fish passage by construction of fish ladders is problematic because upstream passage will commingle native species that were isolated upstream by construction of the dams with non-native species that were introduced subsequently below the dams. Cascading food web interactions elicited by invasions of non-native biota may offset any advantage to native stocks gained by passage and/ or augmentation with hatchery stocks.6. Mitigation must be adaptive in the sense that unanticipated effects and interactions with other management objectives can be documented and alternative action can be implemented.7. This case history of the effects of stream and lake level regulation, and the approaches to management reviewed in this paper, should serve as a lesson in river conservation.

Fish response to modified flow regimes in regulated rivers: research methods, effects and opportunities

“…For example, by improving land use practices (through minimizing deforestation, agricultural expansion, industrialization and urban growth) it is possible to reduce levels of total suspended solids and enhance larval protection in watersheds (Petts, 1990;Mion et al, 1998). A holistic approach would also involve integrating the management of dams on different streams that are within a single watershed (Stanford and Hauer, 1992;Gehrke et al, 1995). Any new structural developments on the river should first undergo comprehensive ecological considerations to provide the flows necessary to sustain the downstream river ecosystem post-development (Petts, 1990;Drinkwater and Frank, 1994).…”

“…Any new structural developments on the river should first undergo comprehensive ecological considerations to provide the flows necessary to sustain the downstream river ecosystem post-development (Petts, 1990;Drinkwater and Frank, 1994). Adaptive management was proposed by several authors as an effective tool for involving stakeholders in addressing aquatic needs in regulated rivers (Stanford and Hauer, 1992;Irwin and Freeman, 2002;Anderson et al, 2006a).…”

Assessment of Climate Change and Freshwater Ecosystems of the Rocky Mountains, Usa and Canada

“…Biota dependent on riparian habitats for portions of their life histories are invariably aected. Rivers downstream of dams experience signi®cant change in hydrographs, thermal characteristics and alteration of zoobenthic and ®sh populations (Stanford and Hauer, 1992). Although most dams are located in intermontane valleys, there is increasing interest in micro-hydroelectric generation in headwater areas.…”

“…The region is dominated by the annual accumulation of winter precipitation as snow and elevated stream¯ows in the late spring and early summer (Po and Ward, 1989). During the 2±3-month`spring runo' period, rivers frequently discharge 470% of their annual water budget and have instantaneous discharges 10±100 times mean low¯ow (Stanford and Hauer, 1992). Changes in the fundamental climatic variables of temperature and precipitation may aect all aspects of the hydrological regime, including water temperature, discharge, nutrient¯ux, groundwater and lake levels, sediment transport, ice and snow cover, biological production, food-web dynamics and biogeography (Firth and Fisher, 1992).…”

River regulation, decline of ecological resources, and potential for restoration in a semi-arid lands river in the western USA

“…The change in discharge is typical of regulated hydrographs that result in measurable negative effects on the ecological structure and function of the river-floodplain corridors (Stanford et al, 1996). These negative effects may be particularly stressful during winter months as aquatic organisms cope with ice cover, reduced movement, and loss of refugia (Sedell et al, 1990;Stanford and Hauer, 1992;Stanford et al, 1996).…”