Non-perennial Streams Research Articles

Integrating intermittent streams into watershed assessments: applicability of an index of biotic integrity

AbstractNonperennial streams are often excluded from biomonitoring programs because of inadequate knowledge about their biological and hydrological characteristics and variability. The ability to apply bioassessment indices to nonperennial streams would greatly expand the reach of biomonitoring programs. We sampled 12 nonperennial streams (3 of which were minimally stressed) in the San Diego hydrologic region multiple times to assess whether a benthic macroinvertebrate assessment index (the Southern California Index of Biotic Integrity [IBI]) developed for perennial streams could be used in nonperennial streams. We also sampled 3 minimally stressed perennial streams. Continuous water-level loggers and repeated site visits revealed that hydrologic regimes varied considerably among streams. Gradual drying was evident at some streams, and multiple drying/rewetting events were evident at others. Moreover, streams that were nonperennial in one year were perennial in another. IBI scores from low-stress nonperen...

Shifts in aquatic macroinvertebrate community structure in response to perenniality, southern Cape, South Africa

Stream flow and associated seasonal hydrologic variation is a critical driver affecting the structure of aquatic macroinvertebrate communities. Quarterly aquatic macroinvertebrate sampling was carried out for a single year along the longitudinal axes of two streams in the southern Cape of South Africa. Stones-in-current, marginal vegetation, gravel-sand-mud, and stones-out-of-current biotopes were sampled for aquatic macroinvertebrates. Associations between macroinvertebrate communities and hydrographs were analyzed to investigate whether a non-perennial stream with greater flow variability had a higher prevalence of common or opportunistic species than a perennial one with less variable flow. Macroinvertebrate species richness was greater in the perennial as opposed to the non-perennial stream, where, on a seasonal basis, species richness increased from winter to autumn. Temporal species turnover differed between sites and streams, where reduced flows transformed the more dominant aquatic biotopes from stones-in-current into standing pools. Findings are that aquatic macroinvertebrates respond to changing flow conditions and reduced mean daily flows resulted in the disappearance of flow-dependant taxa and the arrival of non-flow-dependant taxa.

Identifying Reference Conditions and Quantifying Biological Variability Within Benthic Macroinvertebrate Communities in Perennial and Non-perennial Northern California Streams

Identification of minimally disturbed reference sites is a critical step in developing precise and informative ecological indicators. We tested procedures to select reference sites, and quantified natural variation (inter-site and -annual variability) among reference conditions using a macroinvertebrate data set collected from 429 mediterranean-climate stream reaches in the San Francisco Bay Area, California (USA). We determined that a landscape GIS-based stressor screen followed by a local field-based stressor screen effectively identified least-disturbed reference sites that, based on NMS ordination results, supported different biological communities than sites identified with only landscape (GIS) or local (field) stressors. An examination of least-disturbed reference sites indicated that inter-site variability was strongly associated with stream hydrology (i.e., perennial vs. non-perennial flow) and annual precipitation, which highlights the need to control for such variation when developing biological indicators through natural gradient modeling or using unique biological indicators for both non-perennial and perennial streams. Metrics were more variable among non-perennial streams, indicating that additional modeling may be needed to develop precise biological indicators for non-perennial streams. Among 192 sites sampled two to six times over the 8-year study period, the biological community showed moderate inter-annual variability, with the 100 point index of biotic integrity scores varying from 0 to 51 points (mean = 11.5). Variance components analysis indicated that inter-annual variability explained only a fraction (5-18 %) of the total variation when compared against site-level variation; thus efforts to understand causes of natural variation between sites will produce more precise and accurate biological indicators.

Population ecology of vervet monkeys in a high latitude, semi-arid riparian woodland

Narrow riparian woodlands along non-perennial streams have made it possible for vervet monkeys to penetrate the semi-arid karoo ecosystem of South Africa, whilst artificial water points have more recently allowed these populations to colonize much more marginal habitat away from natural water sources. In order to better understand the sequelae of life in these narrow, linear woodlands for historically ‘natural’ populations and to test the prediction that they are ecologically stressed, we determined the size of troops in relation to their reliance on natural and artificial water sources and collected detailed data from two river-centred troops on activity, diet and ranging behaviour over an annual cycle. In comparison to other populations, our data indicate that river-centred troops in the karoo were distinctive primarily both for their large group sizes and, consequently, their large adult cohorts, and in the extent of home range overlap in what is regarded as a territorial species. Whilst large group size carried the corollary of increased day journey length and longer estimated interbirth intervals, there was little other indication of the effects of ecological stress on factors such as body weight and foraging effort. We argue that this was a consequence of the high density of Acacia karroo, which accounted for a third of annual foraging effort in what was a relatively depauperate floristic habitat. We ascribed the large group size and home range overlap to constraints on group fission.Conservation implications: The distribution of group sizes, sampled appropriately across habitats within a conservation area, will be of more relevance to management than average values, which may be nothing more than a statistical artefact, especially when troop sizes are bimodally distributed.

Drought refuges, spatial scale and recolonisation by invertebrates in non-perennial streams

Summary 1. If resistance traits drive recolonisation after drought, then drought refuges should contribute strongly to assemblage composition within streams. If resilience traits drive recolonisation, macroinvertebrates emerging from refuges may disperse widely, colonising many streams. To determine whether the contribution of drought refuges to macroinvertebrate recolonisation in non-perennial streams was mostly local (within stream) or broader scale (across streams), we measured the association between the composition of invertebrate assemblages in different types of in-stream drought refuge and the assemblage composition of streams when flow resumed. 2. We sampled 16 streams of varying hydrological regime on the western side of the Victoria Range in the Grampians National Park, Victoria, Australia. Drought refuges (perennial pools, dry sediment, damp sediment, seeps, patches of leaf litter, beneath stones) were identified and sampled during autumn. Most taxa were found in perennial pools; few taxa were found aestivating beneath stones or having desiccation-resistant stages in dry sediment. Perennial pools and perennially flowing reaches were the refuges that harboured the greatest diversity of macroinvertebrate taxa. 3. Streams were sampled again during spring. Assemblage composition of non-perennial reaches in spring was unrelated to composition in nearby refuges in the previous autumn. In contrast, assemblage composition in perennial reaches during spring was strongly correlated with composition during autumn. Therefore, drought refuges did not directly influence assemblage composition locally within non-perennial streams. Rather, both perennially flowing reaches and perennial pools acted as drought refuges across the broader landscape. Resilience traits are likely to drive recolonisation in these streams. 4. Monitoring of drought refuges in a particular stream will therefore not predict species composition when flow resumes. Drought refuges are likely to sustain biodiversity over larger spatial scales such as groups of streams or whole drainage networks. Consequently, stream networks will need to be managed as entities rather than as single waterways and the focus of drought refuge protection should be on perennial pools and reaches.

Comparison of Macroinvertebrate Diversity and Community Structure among Perennial and Non-Perennial Headwater Streams

The relationships between stream flow regime and macroinvertebrate diversity, community structure, and functional feeding groups (FFG) were examined to determine if the biodiversity and macroinvertebrate fauna of non-perennial streams are significantly different from those of perennial streams. The study was conducted in northeastern Massachusetts at headwater stream sites of varying flow permanence (perennial, intermittent, and ephemeral). ANOVA confirmed no significant difference in Shannon-Wiener diversity (H′) between stream types, demonstrating that non-perennial streams maintain diverse and even macroinvertebrate communities. Whereas taxa richness was equal among intermittent and perennial sites, ephemeral richness was lower due to their significantly lower riffle richness. Qualitatively, two non-perennial sites were higher in grand total H′ diversity and taxa richness than perennial sites. Community structure was also related to flow regime, as hierarchical cluster analysis (HCA) based on taxa presence produced three distinct groups consistent with stream type, and FFG analysis provided further evidence of distinct communities, with a transition in FFGs from perennial to ephemeral sites. This study concludes that non-perennial streams are biologically diverse and maintain distinct benthic communities and therefore contribute to stream biodiversity and river ecosystems.

Why life history information matters: drought refuges and macroinvertebrate persistence in non-perennial streams subject to a drier climate

In some arid, semi-arid or Mediterranean climate regions, increased water extraction combined with climate change will prolong periods of drought in non-perennial streams, but the effects on macroinvertebrate populations are poorly understood. Drought refuges allow species to survive drying but their use depends on species’ traits, and refuge availability depends on landscape structure. This review evaluates the utility of existing ecological concepts for predicting the role of drought refuges for sustaining biodiversity in non-perennial streams. We also suggest traits that may determine invertebrate species’ resistance or resilience to prolonged drying. Parts of the likely responses by populations to increased stream drying are described by existing ecological concepts, such as the biological traits of species and their interaction with the habitat templet, barriers to dispersal and metapopulation dynamics, the use of drought refuges, habitat fragmentation and population and landscape genetics. However, the limited knowledge of invertebrate life histories in non-perennial streams restricts our ability to use these concepts in a predictive manner. In particular, reach or pool occupancy by species cannot be accurately predicted, but such predictions are necessary for evaluating potential management actions such as the use of environmental flows to sustain drought refuges during dry periods.

Using Markov Chains for Non-perennial Daily Streamflow Data Generation

The use of Markov chains to simulate non-perennial streamflow data is considered. A non-perennial stream may be thought as having three states, namely zero flow, increasing flow and decreasing flow, for which a three-state Markov chain can be constructed. Alternatively, two two-state Markov chains can be used, the first of which represents the existence and non-existence of flow, whereas the second deals with the increment and decrement in the flow for periods with flow. Probabilistic relationships between the two alternatives are derived. Their performances in simulating the state of the stream are compared on the basis of data from two different geographical regions in Turkey. It is concluded that both alternatives are capable of simulating the state of the stream.