Influence of Land Use, and its Change, on Streams and Rivers

Transcription

1 Influence of Land Use, and its Change, on Streams and Rivers Ways in which land use alteration modifies streams. (from JD Allan 2004, Annu. Rev. Ecol., Evol. and Syst.) Dominant types of land use change: 1) Agriculture 2) Urbanization 3) Dams and diversions 1

2 Effects of Agriculture Harding et al. (1998, Proc. Natl. Acad. Sci.): Sampled 12 sites (streams) in each of 2 major watersheds in the southern Appalachians. Used GIS to estimate % riparian forest and % riparian agriculture for each of 24 subwatersheds, i.e., land-cover within a 30-meter buffer strip of stream throughout contributing watershed. In each watershed, 12 sites are now mostly FOREST and 12 sites in substianlly AGRI (Fig.1) TWO Analyses (1) Compare differences in sensitive macroinvertebrate indicators between 12 FOREST and 12 AGRI stream sites based on land-use. (2) Look at land-use history. Are there legacy effects? Are stream biotic conditions influenced by land use? 12 Forested streams in 1990 were >90% forested in 1950s. 12 Agricultural streams in 1990 were 30-60% forested in 1950s but forest regeneration has occurred following agricultural abandonment. (1) Effect of contemporary land-use on macroinvertebrate diversity? Findings: - FOREST sites have average and EPT than AGRI sites. (statistically significant ) - For fish, differences are not as clear because species are not used as the indicator. 2

3 (2) Land-use History: What best predicts macroinvertebrate indicator scores, contemporary land cover or historical land cover? In many sub-watersheds has changed over previous decades, e.g., reforestation of abandoned agriculture. Important finding: (1950) land use better predictor of current biological community than (1990) land use (Table 2). This figure shows similarity of 24 sites in terms invertebrate species composition. What do you see in it? How would you explain that the 2 invert communities in sites are outliers that have species composition that is very similar contemporary streams? These forested streams had about 40 years prior to sampling. The Past historical legacy of prior agricultural land-use Study raises questions about from extensive land use alteration. 3

4 Urbanization and Agriculture (Moore and Palmer 2005) Mixed land uses near Land use affects Washington DC 4 land use classes Richness inversely benthic richness. related to %imperviousness Local riparian buffers (30 m width) improve urban streams but what about Ag? Best management practices explain regional differences in biological condition? Do riparian buffers improve instream ecological condition? Examine 2 studies from agricultural watersheds in Michigan. 1) Roth et al. (1996, Landscape Ecol.) Measured and for 23 stream sites in a Michigan watershed with variable extent of. Watersheds varied from 20% agriculture to 90% agriculture. Question is: Do improve instream habitat quality and IBI scores. 4

5 For each site, measured forest cover at 3 scales: (a) local riparian in the sampling reach, (b) % agriculture in all upstream riparian zone, and (c) % agriculture in entire catchment. and in catchment, but no evidence that improves instream habitat quality. How to explain this lack of correlation with local habitat? (For example, look at point circled in graph.) Note in different catchments. Any about how to detect importance of local ripari 2) Lammert and Allan (1999, Environ. Manage.) - Selected 3 tributaries in agricultural watersheds (42-67% of catchment) explain more variation than variables alone for IBI (fish) and B-IBI Local riparian buffer instream habitat conditions and IBI in agricultural catchments. 5

6 Local riparian buffer improves instream habitat conditions and IBI in heavily agricultural catchments or in heavily urbanized systems? But best management practices in AG lands may improve biological condition Urbanization 6

7 Urbanization The urban stream syndrome (Booth 2005) (Walsh et al. 2005, JNABS) Urban hydrology Streams have (than forested reference ) and often lower base flows. Urban stream has daily mean discharge exceeding annual mean only 29% of time (T qmean ) but higher magnitude. Forested has 39% of time. Low flows often decline with greater (surrogate for urbanization effects) due to loss of and discharge. (Booth 2005) (Roy et al. 2005) 7

8 Urbanization and ecological condition: B-IBI declines with increased urban Are there of imperviousness that cause rapid decline of biotic condition? Evidence for a at 10-15% impervious area? Seattle area (Booth 2005) (Moore & Palmer 2005) Urbanization and ecosystem processes: Fine benthic OM greatly decreased in urban streams, and rate of N and P uptake by biofilm declines. (Meyer et al. 2005) 8

9 Urbanization and fish responses: Fish richness and abundance: - generally declines for. - can increase for. (Table 5) strongly correlated with changes in fish communities (species traits) (Table 7) (For example, endemic species show negative correlation R2=31%) with increased summer stormflows.) (Roy et al. 2005) Urbanization and fish responses: Can depend on natural environmental setting (e.g., Ecoregion). Maryland Fish IBI sensitive to urbanization in PIEDMONT region but not COASTAL PLAIN streams COASTAL PLAIN PIEDMONT Any thoughts why? (Hint: Recall fish IBI in Colorado from last lecture) (Morgan and Cushman 2005) 9

10 The Urban Stream Research Frontier? 1) Better characterization of hydrologic alteration: Most research on urban impacts to streams has concentrated on correlations between instream ecological metrics and total catchment imperviousness. Recent research shows that some of the variance in such relationships can be explained by the distance between the stream reach and urban land, or by the hydraulic efficiency of stormwater drainage. 2) Whole catchment experimentation to identify the best management approaches to conservation and restoration of streams in urban catchments. 3) Restoration? (Walsh et al. 2005) Urban Stream Restoration -- a big challenge Placement of cobble, LWD Burial by sand 8 years later - nice riparian, but no salmon spawning 8 year project in Seattle area (Fig. 3) Adult salmon find urban restored streams but reproductive success is very low (Fig. 5) 10

11 Restoration at national scale? Bernhardt et al. (2005, Science) National River Restoration Science Synthesis (NRRSS) database with ~38,000 projects ( At least $14 to $15 billion spent since 1990 on restoration of streams and rivers (excluding big ticket items such as Glen Canyon, San Francisco Bay, Columbia River, Missouri River, etc.) 11