Riparian Conditions Research Articles

Riparian vegetation as an indicator of riparian condition: Detecting departures from historic condition across the North American West

Floodplain riparian ecosystems support unique vegetation communities and high biodiversity relative to terrestrial landscapes. Accordingly, estimating riparian ecosystem health across landscapes is critical for sustainable river management. However, methods that identify local riparian vegetation condition, an effective proxy for riparian health, have not been applied across broad, regional extents. Here we present an index to assess reach-scale (500 m segment) riparian vegetation condition across entire drainage networks within large, physiographically-diverse regions. We estimated riparian vegetation condition for 53,250 km of perennial streams and rivers, 25,685 km in Utah, and 27,565 km in twelve watersheds of the interior Columbia River Basin (CRB), USA. We used nationally available, existing land cover classification derived from 30 m Landsat imagery (LANDFIRE EVT) and a modeled estimate of pre-European settlement land cover (LANDFIRE BpS). The index characterizes riparian vegetation condition as the ratio of existing native riparian vegetation cover to pre-European settlement riparian vegetation cover at a given reach. Roughly 62% of Utah and 48% of CRB watersheds showed significant (>33%) to large (>66%) departure from historic condition. Riparian vegetation change was predominantly caused by human land-use impacts (development and agriculture), or vegetation change (native riparian to invasive or upland vegetation types) that likely resulted from flow and disturbance regime alteration. Through comparisons to ground-based classification results, we estimate the existing vegetation component of the index to be 85% accurate. Our assessments yielded riparian condition maps that will help resource managers better prioritize sites and treatments for reach-scale conservation and restoration activities.

The Effects of Poplar Plantations on Vascular Plant Diversity in Riparian Landscapes

Riparian vegetation, which performs many key ecological functions, has been modified or lost at an alarming rate during the past century as a result of human activity. The aims of this study are (a) to investigate the effects of poplar plantations on plant diversity in riparian zones; and (b) to estimate the ecological implications of extending cover by poplar plantations. For this purpose, we assessed species richness, habitat indicator species and functional diversity based on Grime’s C-S-R strategies. We used non-metric multidimensional scaling to examine the role of environmental factors such as soil properties, forest structure and management. Disturbance, in particular the frequency of harrowing, led to a decline in species richness and modified the indicator species and functional diversity by favoring Ruderal (R) species at the expense Stress-Tolerant (S) and Competitor (C) species, which are better suited to riparian forest conditions. Poplar plantations should not be used as surrogates for riparian forests, and minimizing harrowing in poplar plantations promotes vascular plant diversity. Furthermore, reintroduction of herbs, ferns and geophytes with a high conservation value and low seed dispersal capacity is advisable from the sixth year after establishment, once harrowing for weed control has been completed.

Riparian vegetation and sediment gradients determine invertebrate diversity in streams draining an agricultural landscape

Separation of natural and anthropogenic influences is required to identify land-use impacts on stream ecosystems. We investigated the effects of water quality and riparian condition on invertebrate assemblages along streams draining agricultural land by partitioning out changes in geomorphological characteristics. There was a strong negative relationship between invertebrate richness and distance downstream, driven by a gradient of reducing stream power and substratum particle size along the streams. When substratum particle size was accounted for, richness was reduced by ∼24% when there was limited availability of coarse particulate organic matter, resulting from lower riparian forest cover upstream. High concentrations of fertilizer-derived nitrate boosted invertebrate abundances, but only in mid sections of streams, where coarse substrata (>100mm) and high insolation were available. Sampling of multiple sites along streams facilitated partitioning of land-use impacts from natural gradients. Invertebrate richness was a good indicator of stream biophysical condition (e.g. nature of the substratum, riparian condition) at the stream scale irrespective of taxonomic resolution (family or higher) or sample size (down to 50 individuals per site), and was therefore a useful monitoring tool. The finding that riparian vegetation is a key determinant of invertebrate diversity should encourage catchment-scale maintenance and rehabilitation of native riparian forest.

Is the Sosiani River Healthy? Investigating the Relationship between Water Quality Indicators and Macroinvertebrate Assemblages in the Sosiani River

The health of rivers is of great concern to governments and communities worldwide due to their important ecological functions. Numerous studies have established that water quality indicators have a positive effect on river health. However, only a few studies have examined equatorial rivers, and, to date, there has been no study on the Sosiani River in Kenya. As such, this study explored the health of the Sosiani River by considering how its aquatic macroinvertebrate assemblages were affected by various water quality parameters. The research considered whether there was a relationship between water quality indicators and macroinvertebrate assemblages in the Sosiani River. This knowledge is of paramount importance to the communities and decision makers of the Sosiani catchment, and Kenya as a whole, since there is need to understand the relationship between the water quality indicators and the health of the river in order to allocate resources for its rehabilitation and maintenance. This study examined 10 sites, nine being “test” sites and one a “reference” site. The study established a significant relationship between water quality parameters and macroinvertebrate assemblages. The sites with natural riparian zone vegetation conditions were found to have more Ephemeroptera, Plecoptera, and Trichoptera macroinvertebrates when compared to those without or with exotic vegetation. In terms of absolute numbers of surface aquatic macroinvertebrates, sites characterised by dense stream bank vegetation had more macroinvertebrates than those characterised by forest with eroded, bare stream banks. From the study, it was therefore concluded that Sosiani River is healthier at head waters where there was natural forests compared to downstream where there was plantations, intensive farming and urban area. The study recommends that more detailed studies classify macroinvertebrates to gunus level and include microinvertebrates, since this may give a more accurate assessment of the river’s health. The study further recommends that identification keys for East African macroinvertebrates be developed.

Anuran Communities in Different Riparian Habitats: Native Forest, Secondary Forest, and Sugarcane

Abstract. This study aimed to test the influence of different riparian habitats on the structure of anuran communities in southeastern Brazil. Nine stream stretches were selected representing three different riparian habitat types: Native Forest, Secondary Forest, and Sugarcane. A total of 223 individuals of 17 species and five families were captured. The Chao1 richness index indicated that after standardizing the sampling effort the Native Forest sites had higher richness than the Secondary Forests and Sugarcane sites, which presented similar richness. The Abundance and Biomass Curves for the Native Forest sites showed an overlap of the weight and abundance curves, suggesting that these sites presented lower disturbance levels. A disturbance gradient from Native Forest towards Sugarcane sites was observed. The Bray-Curtis similarity index showed a significant effect of riparian condition on species composition. Our results suggest that Sugarcane and Secondary Forest sites limit the distribution of certai...

Headcut Erosion in Wyoming's Sweetwater Subbasin.

Increasing human population and intensive land use combined with a warming climate and chronically diminished snowpacks are putting more strain on water resources in the western United States. Properly functioning riparian systems slow runoff and store water, thus regulating extreme flows; however, riparian areas across the west are in a degraded condition with a majority of riparian systems not in proper functioning condition, and with widespread catastrophic erosion of water-storing peat and organic soils. Headcuts are the leading edge of catastrophic channel erosion. We used aerial imagery (1.4-3.3-cm pixel) to locate 163 headcuts in riparian areas in the Sweetwater subbasin of central Wyoming. We found 1-m-the generally available standard resolution for land management-and 30-cm pixel imagery to be inadequate for headcut identification. We also used Structure-from-Motion models built from ground-acquired imagery to model 18 headcuts from which we measured soil loss of 425-720 m3. Normalized by channel length, this represents a loss of 1.1-1.8 m3 m(-1) channel. Monitoring headcuts, either from ground or aerial imagery, provides an objective indicator of sustainable riparian land management and identifies priority disturbance-mitigation areas. Image-based headcut monitoring must use data on the order of 3.3 cm ground sample distance, or greater resolution, to effectively capture the information needed for accurate assessments of riparian conditions.

Predicting fecal indicator organism contamination in Oregon coastal streams

In this study, we used publicly available GIS layers and statistical tree-based modeling (CART and Random Forest) to predict pathogen indicator counts at a regional scale using 88 spatially explicit landscape predictors and 6657 samples from non-estuarine streams in the Oregon Coast Range. A total of 532 frequently sampled sites were parsed down to 93 pathogen sampling sites to control for spatial and temporal biases. This model's 56.5% explanation of variance, was comparable to other regional models, while still including a large number of variables. Analysis showed the most important predictors on bacteria counts to be: forest and natural riparian zones, cattle related activities, and urban land uses. This research confirmed linkages to anthropogenic activities, with the research prediction mapping showing increased bacteria counts in agricultural and urban land use areas and lower counts with more natural riparian conditions.

From past patterns to future potential: using historical ecology to inform river restoration on an intermittent California river

Effective river restoration requires understanding a system’s potential to support desired functions. This can be challenging to discern in the modern landscape, where natural complexity and heterogeneity are often heavily suppressed or modified. Historical analysis is therefore a valuable tool to provide the long-term perspective on riverine patterns, processes, and ecosystem change needed to set appropriate environmental management goals and strategies. In this study, we reconstructed historical (early 1800s) riparian conditions, river corridor extent, and dry-season flow on the lower Santa Clara River in southern California, with the goal of using this enhanced understanding to inform restoration and management activities. Hundreds of cartographic, textual, and visual accounts were integrated into a GIS database of historical river characteristics. We found that the river was characterized by an extremely broad river corridor and a diverse mosaic of riparian communities that varied by reach, from extensive (>100 ha) willow-cottonwood forests to xeric scrublands. Reach-scale ecological heterogeneity was linked to local variations in dry-season water availability, which was in turn underpinned by regional geophysical controls on groundwater and surface flow. Although human actions have greatly impacted the river’s extent, baseflow hydrology, and riparian habitats, many ecological attributes persist in more limited form, in large part facilitated by these fundamental hydrogeological controls. By drawing on a heretofore untapped dataset of spatially explicit and long-term environmental data, these findings improve our understanding of the river’s historical and current conditions and allow the derivation of reach-differentiated restoration and management opportunities that take advantage of local potential.

Comparison of decapod communities across an urban-forest land use gradient in Puerto Rican streams

Urbanization influences a range of factors related to stream health, including the hydrologic regime, water quality, and riparian conditions that lead to negative effects on terrestrial and aquatic ecosystems. However, impacts on freshwater decapods from urbanization of tropical streams have not been reported. We hypothesized that changes in decapod communities in watersheds with different levels of urbanization are related to changes in physical stream habitats caused by different land uses and their effects on water discharge. The impacts of land use on the physico-chemical characteristics of streams and freshwater decapod communities were evaluated in three watersheds characterized by low, moderate and high-intensities of urbanization in Puerto Rico. For the low and moderately developed urban watersheds, decapod species richness ranged from 10 to 11 species; the highly urbanized watershed only had 4 species. Macrobrachium faustinum and Xiphocaris elongata were the most ubiquitously species and were found in all watersheds. Multivariable analysis of physical characteristics and densities of the decapod families resulted in one axis that explained 80 % of the total variation among the watersheds and was correlated with stream discharge. The effect of discharge is likely a result of frequent high flows that sustain habitats with high concentrations of dissolved oxygen and low concentrations of pollutants. An increase in physico-chemical parameters were observed from the LUW to the HUW. These results indicate that the decapod communities were most likely influenced by land use and environmental conditions that affected erosional aspects related to water discharge and water quality in the highly impacted watersheds.

Abiotic features of a river from the Upper Tietê River Basin (SP, Brazil) along an environmental gradient

Aim: This study aimed to assess the spatial and seasonal variation of the water quality and physical habitat characteristics along the upper-middle stretch of the Paraitinga River, a tributary of Tietê River, considering the potential influence of different riparian conditions along the stretch studied.MethodsSixteen sites with different riparian vegetation, including native forest, secondary forest, pasture, and eucalyptus were sampled during the dry and rainy seasons of 2004/2005, before the damming of the Paraitinga Reservoir. Several physicochemical and habitat parameters were determined and data analyzed in relation to spatial distribution and potential influence of riparian conditions.ResultsWater quality parameters were in general within the limits established by CONAMA for Class 2 waters, except for turbidity and total phosphorus. There were seasonal and spatial differences in the limnological parameters along the stretch studied and apparently they were related to point specific influences associated with land use and canopy cover. Habitat characteristics were markedly different between the upper and middle river stretches, especially in relation to depth, width, substrate and canopy cover.ConclusionsAlthough a direct influence on the observed variables could not be attributed solely to the riparian vegetation, vegetation cover seemed to affect particular stream characteristics. Open pasture and eucalyptus sites were subject to point specific effects that caused phosphorus inputs and higher turbidity and temperature, and showed different morphological features, suggesting that land use at the sub-watershed scale was an important factor affecting stream conditions.

A Fish-Based Index of Biotic Integrity for the Assessment of Streams Located in a Sugarcane-Dominated Landscape in Southeastern Brazil.

A multimetric, fish-based Index of Biotic Integrity (IBI) was developed and tested to assess the ecological status of streams with different riparian conditions in the Piracicaba River Basin. Nine streams with three categories of riparian zone preservation were selected: native forest (NF) with preserved forest, secondary forest (SF) with forest in an advanced state of regeneration and surrounded by sugarcane plantations, and sugarcane (SC) without riparian vegetation and surrounded by SC crops. A continuous scoring system was employed, and candidate metrics were tested for range, responsiveness, and redundancy, resulting in the selection of eight metrics to compose the index. The final IBI score was positively correlated with an Environmental Index both in the dry (Spearman's rho = 0.76; P = 0.01) and rainy seasons (Spearman's rho = 0.66; P = 0.04), suggesting that this IBI is a suitable tool for the assessment of the biological conditions of these streams. The highest IBI values were observed in the rainy season at the NF and SF sites, with significant differences between the NF and SC sites (Kruskal-Wallis test: P = 0.03). The results indicated some variability in the biological integrity at SF and SC sites, suggesting a relationship with the intensity of the management of this crop. Patterns were consistent with other studies that have shown the effects of agriculture on the environmental quality of streams, which indicate the importance of the riparian zone to the maintenance of ecosystem integrity and supports the use of the IBI for biological monitoring in similar regions.

Assessing the importance of the riparian zone for stream fish communities in a sugarcane dominated landscape (Piracicaba River Basin, Southeast Brazil)

In the Neotropics, the effect of agriculture on freshwater habitats is still poorly understood, particularly with respect to sugarcane expansion to meet increased ethanol demands. The variation in taxonomic composition, community attributes and trophic structure of fish assemblages from streams under different riparian zone preservation conditions were studied. Nine stream reaches under the following riparian vegetation conditions were selected: Native Forest (NF), with mostly primary forest; Secondary Forest (SF), which included sites with vegetation in an advanced stage of regeneration surrounded by sugarcane plantations; and Sugarcane sites (SC), located in areas without riparian vegetation, adjacent to sugarcane crops. Forty-one species were collected. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that community composition and trophic structure were significantly explained by riparian condition and spatial variations, while diversity, richness, abundance and biomass were only explained by season and space, with higher diversity and richness at the SF sites. Abundance-Biomass curves (ABC curves) suggested that sugarcane plantations destabilized fish assemblages, especially at the more intensively managed sites, which seem to influence stream integrity and associated fish fauna. We concluded that both physical conditions of streams and some attributes of fish communities reflected the different levels of preservation of the riparian buffers, but given the influence of regional processes which have a pervasive role in shaping local assemblages, land use at the watershed scale seemed to be important especially to explain the higher richness and diversity found at the SF sites.

Habitat suitability modelling of rare species using Bayesian networks: Model evaluation under limited data

Paucity of data on rare species is a common problem, preventing the use of most approaches to model development and evaluation. This study demonstrates how models can be developed and different forms of evaluation can be performed despite a lack of sufficient data, by presenting a habitat suitability model for the rare Astacopsis gouldi, the giant freshwater crayfish. We use a Bayesian network approach that readily incorporates incomplete data and allows for the evaluation of uncertainties. To supplement the limited field data on A. gouldi, expert knowledge was elicited through surveys designed to provide probability values that described the strength of relationships between the habitat suitability of the species and three variables – elevation, upstream riparian condition and geomorphic condition – and credible intervals around those values. A series of 18 alternative models were developed based on the same model structure but parameterised using different sources – expert judgement, field data or a combination of the two. The models were evaluated by estimating and comparing their performance accuracy and sensitivity analysis results, and in assessing the assumptions underpinning each of the models. Using performance accuracy as a measure, the data-based and combined expert- and data-based models performed better than the expert-based models. The sensitivity analysis results show that geomorphic condition was the most influential variable in the majority of models and that elevation had minimal influence on the occurrence of A. gouldi. Overall the models were found to have large predictive uncertainties, although the modelling process itself revealed insights into the habitat suitability of the species and identified key knowledge and data gaps for future monitoring, management and research.

Reach-Scale Comparison of Habitat and Mollusk Assemblages for Select Sites in the Clinch River with Regional Context

Several hypotheses, including habitat degradation and variation in fluvial geomorphology, have been posed to explain extreme spatial and temporal variation in Clinch River mollusk assemblages. We examined associations between mollusk assemblage metrics (richness, abundance, recruitment) and physical habitat (geomorphology, streambed composition, fish habitat, and riparian condition) at 10 sites selected to represent the range of current assemblage condition in the Clinch River. We compared similar geomorphological units among reaches, employing semi-quantitative and quantitative protocols to characterize mollusk assemblages and a mix of visual assessments and empirical measurements to characterize physical habitat. We found little to no evidence that current assemblage condition was associated with 54 analyzed habitat metrics. When compared to other sites in the Upper Tennessee River Basin (UTRB) that once supported or currently support mollusk assemblages, Clinch River sites were more similar to each other, representing a narrower range of conditions than observed across the larger geographic extent of the UTRB. A post-hoc analysis suggested stream size and average boundary shear stress at bankfull stage may have historically limited species richness in the UTRB (p < 0.001). Associations between mollusk assemblages and physical habitat in the UTRB and Clinch River currently appear obscured by other factors limiting richness, abundance, and recruitment.

Macroinvertebrate functional feeding groups in Kenyan highland streams: evidence for a diverse shredder guild

AbstractData on the functional composition of invertebrates in tropical streams are needed to develop models of ecosystem functioning and to assess anthropogenic effects on ecological condition. We collected macroinvertebrates during dry and wet seasons from pools and riffles in 10 open- and 10 closed-canopy Kenyan highland streams. We classified macroinvertebrates into functional feeding groups (FFGs), which we used to assess effects of riparian condition and season on functional organization. We used cluster analysis of gut contents to classify 86 taxa as collectors, predators, scrapers, or shredders. We classified 23 taxa whose guts were empty or had indistinguishable contents based on literature. In total, we identified 43 predators, 26 collectors, 19 scrapers, and 19 shredders. Total abundance was higher in open-canopy agricultural streams, and species richness was higher in closed-canopy forested streams. Predators and shredders dominated richness and biomass, respectively, in the closed-canopy stre...

Changes in Structure and Function of Fish Assemblages along Environmental Gradients in an Intensive Agricultural Region of Subtropical Taiwan

Intensive agriculture has degraded streams in subtropical Taiwan, but agricultural impacts on fish assemblages are not well studied. The goal of this study was to understand changes in structure and function of fish assemblages along environmental gradients in an agricultural region of South-central Taiwan. Nineteen sites in the hill and upper plain regions were selected for fish sampling during the base flow period. Water chemistry analyses and rapid habitat assessment were also conducted. Cluster analysis separated fish assemblages into four assemblage groups and a single site. A redundancy analysis (RDA) showed that environmental variables explained 73.9% of species variance. RDA axis 1 represented a habitat-diversity, cover, and nutrient gradient, whereas RDA axis 2 represented a complex riparian condition gradient. Relative abundances of dominant fish species and assemblage groups were related to water and habitat variables. Trophic and tolerance guilds were correlated with RDA axes. Number of fish species increased with decreasing elevation. Both structure and function of fish assemblages changed with water and habitat gradients in these subtropical agricultural streams.

Ecological opportunities and intraspecific competition alter trophic niche specialization in an opportunistic stream predator

Many generalist populations are composed of specialized individuals that use a narrow part of the population's niche. Ecological theories predict that individual specialization and population trophic niche are determined by biotic interactions and resource diversity emerging from environmental variations (i.e. ecological opportunities). However, due to the paucity of empirical and experimental demonstrations, the genuine importance of each of these drivers in determining trophic niche attributes is not fully appreciated. The present study aimed at determining the population level and individual responses of brown trout (Salmo trutta) to variations in ecological opportunities (terrestrial prey inputs) and autochthonous prey communities among 10 stream reaches along a riparian condition gradient using individual longitudinal monitoring and stable isotope analyses. Our results suggested that trophic niche diversity varied along the environmental gradient, while individual trophic specialization was indirectly driven by ecological opportunities through strengthened intraspecific competition. Individual diet was repeatable over the study period, and the growth rate of juvenile brown trout increased with their specialization for aquatic predatory invertebrates. Our findings highlight the dual influences of intraspecific competition and ecological opportunities on individual trophic specialization and population trophic niche.

Influence of riparian quality on macroinvertebrate assemblages in subtropical mountain streams

The type and extent of riparian vegetation is known to have a significant influence on macroinvertebrate communities. The objective of this work was to assess the influence of the quality of a subtropical riparian forest on the structure and composition of macroinvertebrate assemblages. Lower diversity and richness of invertebrates has been found in degraded reaches in comparison with native forested sites. Richness, diversity and density of collector-gatherers were sensitive to the quality of riparian vegetation. Native riparian species at sites of good riparian quality contribute to greater habitat complexity and higher quantities of palatable food, determining the differences in the structure of macroinvertebrate assemblages between sites. This work suggests the use of the IBY-4 index in future management studies of Yungas streams because of its sensitivity to changes in riparian conditions.

Assessment of the crop coefficient for saltgrass under native riparian field conditions in the desert southwest

Limited urban water supplies in southwestern USA cause water managers and planners to re-assess water losses and needs from consumptive water use by riparian vegetation. Here, we report on field measurements of evapotranspiration (ET) for inland saltgrass [Distichlis spicata var. stricta (L.) Greene]; a once common riparian plant native to the desert southwest. The objective was to develop a saltgrass crop coefficient, Kc, similar to agricultural crop coefficients commonly used in irrigation water management. The developed Kc, in conjunction with the local climate, can then be used to assess the water savings that may be achieved in riparian zones for saltgrass versus invasive species and for use in irrigation management and scheduling of saltgrass in urban setting. The ET of saltgrass was measured in its native riparian setting located in the flood plain of the Rio Grande, north of Caballo Lake, New Mexico, in 2011 using an eddy covariance technique in the energy budget method. Total ET of 692 mm was measured during the growing season (n = 241 days) and 837 mm during the year. The American Society of Civil Engineers standardized ET for short crop (ETso) was calculated using climate data measured at the study site as 1560 mm during the growing season and 1870 mm during the year. Crop coefficients (ET/ETso) were fitted with a polynomial equation as a function of day of the year to develop saltgrass Kc function. A graphical and simplified method of computing Kc as a function of day of the year and crop season was also developed as an alternative method. Copyright © 2013 John Wiley & Sons, Ltd.

Butterfly Assemblages Associated with Invasive Tamarisk (Tamarix spp.) Sites: Comparisons with Tamarisk Control and Native Vegetation Reference Sites

We studied butterfly assemblages at six types of riparian landscapes in five different watersheds in the southwestern United States (n=34 sites). Sites included exotic-invasive Tamarix ramosissima (tamarisk) dominated sites; sites where tamarisk was controlled, but not actively revegetated; sites revegetated with upland plants; sites where control was followed with riparian plant revegetation; native riparian vegetation sites; and sites that were a mixture of native and tamarisk vegetations. Local butterfly species were linked regionally by identifying species consisting of more sensitive butterflies that are less resilient to vegetation changes and environmental perturbations and then identifying a subgroup that was reported from all watersheds. This allowed for a regional assessment relevant to all watersheds. Significant differences were found between the abundance of these in-common disturbance sensitive species at different landscapes. Sites where tamarisk was removed without restoration had butterfly metrics similar to the low values at tamarisk sites. The assumption that tamarisk removal is sufficient to recover sensitive species was not true in cases we examined. Soil moisture and riparian condition were identified as important variables associated with abundance of more sensitive butterfly species. Results support the importance of reinstating stream-flow regimes and suggest active restoration of sites if sensitive riparian wildlife species are desired.