Duration Of Low Flows Research Articles

Antecedent flow conditions and nitrate concentrations in the Mississippi River basin

Abstract. The relationship between antecedent flow conditions and nitrate concentrations was explored at eight sites in the 2.9 million square kilometers (km2) Mississippi River basin, USA. Antecedent flow conditions were quantified as the ratio between the mean daily flow of the previous year and the mean daily flow from the period of record (Qratio), and the Qratio was statistically related to nitrate anomalies (the unexplained variability in nitrate concentration after filtering out season, long-term trend, and contemporaneous flow effects) at each site. Nitrate anomaly and Qratio were negatively related at three of the four major tributary sites and upstream in the Mississippi River, indicating that when mean daily streamflow during the previous year was lower than average, nitrate concentrations were higher than expected. The strength of these relationships increased when data were subdivided by contemporaneous flow conditions. Five of the eight sites had significant negative relationships (p ≤ 0.05) at high or moderately high contemporaneous flows, suggesting nitrate that accumulates in these basins during a drought is flushed during subsequent high flows. At half of the sites, when mean daily flow during the previous year was 50 percent lower than average, nitrate concentration can be from 9 to 27 percent higher than nitrate concentrations that follow a year with average mean daily flow. Conversely, nitrate concentration can be from 8 to 21 percent lower than expected when flow during the previous year was 50 percent higher than average. Previously documented for small, relatively homogenous basins, our results suggest that relationships between antecedent flows and nitrate concentrations are also observable at a regional scale. Relationships were not observed (using all contemporaneous flow data together) for basins larger than 1 million km2, suggesting that above this limit the overall size and diversity within these basins may necessitate the use of more complicated statistical approaches or that there may be no discernible basin-wide relationship with antecedent flow. The relationships between nitrate concentration and Qratio identified in this study serve as the basis for future studies that can better define specific hydrologic processes occurring during and after a drought (or high flow period) which influence nitrate concentration, such as the duration or magnitude of low flows, and the timing of low and high flows.

HABITAT USE OF AN ENDEMIC MOLLUSC ASSEMBLAGE IN A HYDROLOGICALLY ALTERED REACH OF THE SNAKE RIVER, IDAHO, USA

Major waterways have been dramatically altered by dams some of which have operated with consistent and significant flow alterations annually since the early 1900s. Re-operation strategies are increasingly being considered for such dams in regions where biodiversity hotspots of sensitive taxa remain. Understanding the impacts of current dam operations on sensitive species is vital to designing re-operations that effectively promote species conservation. Our objectives were to examine the effects of consistent and dramatic flow alterations from a major dam on the distribution of a highly diverse endemic mollusc assemblage in the middle Snake River, Idaho, USA. Quarter metre plots were surveyed along transects with a Venturi suction dredge and classified as permanently or seasonally wetted habitat by depth. Species were classified by degree of endemism. Chi-square analysis was used to compare species presence between habitat types and analysis of variance was used to assess the significance of habitat type as a predictor of mollusc abundance, species richness and Shannon's H. Multivariate analyses were used to investigate mollusc assemblage composition and correlations with environmental parameters. The majority of mollusc species, including species of conservation concern, were found more frequently and in greater abundance in permanently wetted habitat. In addition, the mollusc assemblage in permanently wetted habitat was more diverse. Species presence and abundance patterns were consistent with source sink population dynamics with permanently wetted habitat serving as a source for seasonally wetted habitat. Results indicate that most mollusc species do not use seasonally wetted habitat even four months after it becomes available despite viable environmental conditions, highly mobile species and colonization sources. Our findings suggest that dam re-operations which reduce the magnitude and duration of seasonal low flows may improve habitat availability for sensitive benthic assemblages. Copyright © 2013 John Wiley & Sons, Ltd.

The groundwater recharge response and hydrologic services of tropical humid forest ecosystems to use and reforestation: Support for the “infiltration-evapotranspiration trade-off hypothesis”

Summary The hydrologic effects of forest use and reforestation of degraded lands in the humid tropics has implications for local and regional hydrologic services but such issues have been relatively less studied when compared to the impacts of forest conversion. In particular, the “infiltration-evapotranspiration trade-off” hypothesis which predicts a net gain or loss to baseflow and dry-season flow under both, forest degradation or reforestation depending on conditions has not been tested adequately. In the Western Ghats of India, we examined the hydrologic responses and groundwater recharge and hydrologic services linked with three ecosystems, (1) remnant tropical evergreen forest (NF), (2) heavily-used former evergreen forest which now has been converted to tree savanna, known as degraded forest(DF), and (3) exotic Acacia plantations (AC, Acacia auriculiformis) on degraded former forest land. Instrumented catchments ranging from 7 to 23 ha representing these three land-covers (3 NF, 4 AC and 4 DF, in total 11 basins), were established and maintained between 2003 and 2005 at three sites in two geomorphological zones, Coastal and Up-Ghat (Malnaad). Four larger (1–2 km2) catchments downstream of the head-water catchments in the Malnaad with varying proportions of different land-cover and providing irrigation water for areca-nut and paddy rice were also measured for post-monsoon baseflow. Daily hydrological and climate data was available at all the sites. In addition, 36 min data was available at the Coastal site for 41 days as part of the opening phase of the summer monsoon, June–July 2005. Low potential and actual evapotranspiration rates during the monsoon that are similar across all land-cover ensures that the main control on the extent of groundwater recharge during the south-west monsoon is the proportion of rainfall that is converted into quick flow rather than differences in evapotranspiration between the different land cover types. The Flow duration curves demonstrated a higher frequency and longer duration of low flows under NF when compared to the other more disturbed land covers in both the Coastal and Malnaad basins. Groundwater recharge estimated using water balance during the wet-season in the Coastal basins under NF, AC and DF was estimated to be 50%, 46% and 35% respectively and in the Malnaad it was 61%, 55% and 36% respectively. Soil Water Infiltration and Movement (SWIM) based recharge estimates also support the pattern (46% in NF; 39% in AC and 14% in DF). Furey–Gupta filter based estimates associated with the Coastal basins also suggest similar groundwater recharge values and trends across the respective land-covers: 69% in NF, 49% in AC, and 42% in DF. Soil water potential profiles using zero flux plane methods suggest that during the dry-season, natural forests depend on deep soil moisture and groundwater. Catchments with higher proportion of forest cover upstream were observed to sustain flow longer into the dry-season. These hydrologic responses provide some support towards the “infiltration-evapotranspiration trade-off” hypothesis in which differences in infiltration between land-cover rather than evapotranspiration determines the differences in groundwater recharge, low flows and dry-season flow. Groundwater recharge is the most temporally stable under natural forest, although substantial recharge occurs under all three ecosystems, which helps to sustain dry-season flow downstream in higher order streams that sustain local communities and agro-ecosystems. In addition to spatial scale effects, greater attention also needs to be given to the role of hydrogeology within the context of the above hypothesis and its implications for hydrologic services.

Fish recruitment in rivers with modified discharge depends on the interacting effects of flow and thermal regimes

Summary Alteration of flow and thermal regimes is a key consequence of human use of river and floodplain ecosystems, and these impacts result from a range of interacting ecological mechanisms. Environmental flow regimes are a management strategy to restore or maintain ecologically important aspects of river hydrology. However, inadequate understanding of the processes that determine the effects of flow on population dynamics of biota hinders the maximum benefits of environmental flows. Spawning and recruitment of riverine fish is mediated by temperature, access to nursery habitat and the timing and availability of resources. Differences in population sizes between regulated and unregulated rivers are often attributed to the effect of flow and thermal regime change on population dynamics. Dams and extraction of water have altered the flow and thermal regimes of rivers in the northern Murray–Darling Basin, Australia. Combining three studies, we (i) examined differences in the recruitment of fish and patterns of potential prey availability between a regulated and unregulated river, (ii) studied the relationships between patterns of flow and temperature on spawning of fish in two rivers with contrasting regulated flow regimes and (iii) experimentally tested the effects of environmental flow releases in a regulated river on fish spawning and recruitment by comparing patterns over time against two unregulated rivers. Comparisons between regulated and unregulated rivers indicated that the significantly lower recruitment of Macquaria ambigua in the regulated river was linked with large differences in available prey. Species‐specific differences in the abundance of fish larvae between two regulated rivers indicated that different reproductive strategies determine population‐level responses to flow regulation. Finally, the experimental flow releases in a regulated reach during late spring did not result in a change in spawning and recruitment of fish, although influences of antecedent flow and temperature on larval and juvenile assemblage composition were significant. These findings indicate that the responses of fish spawning and recruitment to flow regime change and restoration are dependent on the conditions that determine the success of these critical life‐history processes. Specifically, key effects of flow regulation are reduced summer water temperatures due to hypolimnetic discharge from dams, and the reduced frequency and duration of low flows. Reduced water temperatures limit opportunities for fish to spawn, and sustained base flows were associated with lower densities of potential prey sources in conjunction with potential flushing of larvae and juveniles, thereby influencing recruitment. The benefits of environmental flow programmes can be enhanced if flow regimes are modified to ensure that abiotic and biotic conditions that support persistence of biota are provided. In conjunction with flow pulses and floods, low flows are a natural and ecologically important component of flow regimes, particularly in dryland rivers. Understanding the interactive and mechanistic effects of flow and thermal regimes on population viability and patterns of biodiversity is critical to maximising the value of environmental flows.

Alteration of flow regimes caused by large‐scale forest disturbance: a case study from a large watershed in the interior of British Columbia, Canada

ABSTRACTForest disturbance can greatly alter flow regimes and consequently the structures and functions of ecosystems. However, the impacts of forest disturbance on flow regimes have rarely been investigated in large watersheds. In this study, we used a large severely disturbed watershed, the Baker Creek watershed located in the central interior of British Columbia, Canada, to examine how forest disturbance altered the flow regimes and to discuss the possible ecological implications of these alterations. Equivalent clear‐cut area, an indicator combining all types of forest disturbances and accounting for hydrological recovery, was adopted to represent the cumulative forest disturbance levels over time at a watershed scale. Flow duration curves and time series cross‐correlation analysis were used to detect the statistical significance of relationships between flow regimes (magnitude, duration, timing, frequency and variability of high flows and low flows) and forest disturbance (clear‐cut area). The results showed that the magnitude of high flows was significantly increased and the timing of high flows was significantly advanced by forest disturbance. After forest disturbance, the occurrence of high flows with greater return periods became more frequent with increased variations. In addition, forest disturbance significantly increased the magnitude of low flows but with reduced variability. On average, high flows and low flows in the disturbed period were 31·4% and 16·0% greater than those in the reference period, respectively. Possible ecological implications of these hydrological alterations caused by forest disturbance were also discussed. Copyright © 2013 John Wiley & Sons, Ltd.

Dissolved nutrient retention dynamics in river networks: A modeling investigation of transient flows and scale effects

We have used a dynamic hydrologic network model, coupled with a transient storage zone solute transport model, to simulate dissolved nutrient retention processes during transient flow events at the channel network scale. We explored several scenarios with a combination of rainfall variability, and biological and geomorphic characteristics of the catchment, to understand the dominant factors that control the transport of dissolved nutrients (e.g., nitrate) along channel networks. While much experimental work has focused on studying nutrient retention during base flow periods in headwater streams, our model‐based theoretical analyses, for the given parameter combinations used, suggest that high‐flow periods can contribute substantially to overall nutrient retention, and that bulk nutrient retention is greater in larger rivers compared to headwaters. The relative efficiencies of nutrient retention during high‐ and low‐flow periods vary due to changes in the relative sizes of the main channel and transient storage zones, as well as due to differences in the relative strengths of the various nutrient retention mechanisms operating in both zones. Our results also indicate that nutrient retention efficiency at all spatial scales of observation has strong dependence on within‐year variability of streamflow (e.g., frequency and duration of high and low flows), as well as on the relative magnitudes of the coefficients that govern biogeochemical uptake processes: the more variable the streamflow, the greater the export of nutrients. Despite limitations of the model parameterizations, our results suggest that increased attention must be paid to field observations of the interactions between process hydrology and nutrient transport and reaction processes at a range of scales to assist with extrapolation of understandings and estimates gained from site‐specific studies to ungauged basins across gradients in climate, human impacts, and landscape characteristics.

Long‐Term Dynamics of Native and Nonnative Fishes in the San Juan River, New Mexico and Utah, under a Partially Managed Flow Regime

AbstractNonnative fishes and flow alteration are primary threats to native fish persistence in lotic systems. We used several flow regime attributes and fish sampling data obtained from the San Juan River, New Mexico and Utah, during 1993–2010 to evaluate the potential use of flow manipulations to increase recruitment of native fishes that must cope with nonnative species. During this period, discharge in the river was partially manipulated by reservoir releases that augmented naturally high spring flows in this snowmelt‐driven system. An information theoretic approach was used to rank candidate models that predicted species densities based upon selected combinations of flow attributes and abundances of nonnative species. Autumn density of age‐0 fishes in secondary channels was the main response variable. The main predictor variables included flow attributes associated with interannual variation in daily discharge and water temperature; densities of nonnative competitors; and catch rates of a numerically dominant nonnative predator (the channel catfish Ictalurus punctatus). Top‐ranked models for native species included positive associations with small‐bodied nonnative fishes and negative associations with the abundance of channel catfish adults. Densities of native speckled dace Rhinichthys osculus and flannelmouth suckers Catostomus latipinnis increased with mean spring discharge, but the density of native bluehead suckers C. discobolus did not. With the exception of juvenile channel catfish, the top candidate models predicting densities of nonnative fishes all included the duration of low summer flows. These results confirmed findings from a previous study that demonstrated different responses of native and nonnative fishes to seasonal flows; the present study also revealed that densities of all fishes were generally lower in years with greater abundance of adult channel catfish. Regression analysis indicated that seasonal flow manipulations and suppression of nonnative predator populations could be effective management tools to restore and maintain the native fish community.

RELATIONSHIPS BETWEEN RIVER DISCHARGE AND ABUNDANCE OF AGE 0 REDHORSES (MOXOSTOMA SPP.) IN THE OCONEE RIVER, GEORGIA, USA, WITH IMPLICATIONS FOR ROBUST REDHORSE

ABSTRACTRobust redhorse (Moxostoma robustum) and notchlip redhorse (M. collapsum) are two species of redhorses that reside in the lower Oconee River, Georgia. Robust redhorse is listed as a state endangered species in Georgia and North Carolina, and attempts to investigate factors affecting its reproductive success have met with limited success. Therefore, catch of robust redhorse young were combined with catch of notchlip redhorse to increase sample size. These congeners with similar spawning repertoire were assumed to respond similarly to environmental conditions. River discharge during spawning and rearing seasons may affect abundance of both redhorses in the lower Oconee River. An information‐theoretic approach was used to evaluate the relative support of models relating abundance of age 0 redhorses to monthly discharge statistics that represented magnitude, timing, duration, variability and frequency of river discharge events for April through June 1995–2006. The best‐approximating model indicated a negative relationship between the abundance of redhorses and mean maximum river discharge and the number of high pulses during June as well as a positive relationship with intermediate duration of low flows during April–June. This model is 9.6 times more plausible than the next best‐fitting model, which revealed a negative relationship between the abundance of redhorses and mean maximum river discharge during May and the number of high pulses during June as well as a positive relationship between abundance and intermediate duration of low flows during April–June. Management implications from the results indicate low‐stable flows for at least a 2‐week period during spawning and rearing may increase reproductive success of robust and notchlip redhorses. Copyright © 2012 John Wiley & Sons, Ltd.

Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins

Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes and variability of flow regimes.

Investigating hydrologic alteration as a mechanism of fish assemblage shifts in urbanizing streams

Stream biota in urban and suburban settings are thought to be impaired by altered hydrol- ogy; however, it is unknown what aspects of the hydrograph alter fish assemblage structure and which fishes are most vulnerable to hydrologic alterations in small streams. We quantified hydrologic variables and fish assemblages in 30 small streams and their subcatchments (area 8-20 km 2 ) in the Etowah River Catchment (Georgia, USA). We stratified streams and their subcatchments into 3 landcover categories based on imperviousness (,10%, 10-20%, .20% of subcatchment), and then estimated the degree of hydrologic alteration based on synoptic measurements of baseflow yield. We derived hydrologic variables from stage gauges at each study site fo r1y( January 2003-2004). Increased imperviousness was positively correlated with the frequency of storm events and rates of the rising and falling limb of the hydrograph (i.e., storm ''flashiness'') during most seasons. Increased duration of low flows associated with impervi- ousness only occurred during the autumn low-flow period, and this measure corresponded with increased richness of lentic tolerant species. Altered storm flows in summer and autumn were related to decreased richness of endemic, cosmopolitan, and sensitive fish species, and decreased abundance of lentic tolerant species. Species predicted to be sensitive to urbanization, based on specific life-history or habitat require- ments, also were related to stormflow variables and % fine bed sediment in riffles. Overall, hydrologic variables explained 22 to 66% of the variation in fish assemblage richness and abundance. Linkages be- tween hydrologic alteration and fish assemblages were potentially complicated by contrasting effects of elevated flows on sediment delivery and scour, and mediating effects of high stream gradient on sediment delivery from elevated flows. However, stormwater management practices promoting natural hydrologic regimes are likely to reduce the impacts of catchment imperviousness on stream fish assemblages.

Relationship between flow regime and fish abundances in a gravel‐bed river, New Zealand

The key elements of the flow regime of the Waipara River on the east coast of New Zealand, that affected fish abundances were the timing of floods and the magnitude and duration of low flows. Generally, fish abundances were highest in early summer, and lowest at the beginning of winter. Spring floods opened the river mouth, allowing recruitment of diadromous fish species, and non‐diadromous fish species spawned after the floods in spring or early summer. Reductions in fish abundances over summer and autumn were consistent with the magnitude and duration of low flows, with significant reductions in the year of lowest flow and little change in abundance in the year when low flows were highest. Variations in fish abundances during periods of low flow were consistent with the amount of instream habitat available, such that abundances of species with high velocity preferences decreased during periods of low flow, whereas abundances of species with low velocity preferences increased.

Investigating hydrologic alteration as a mechanism of fish assemblage shifts in urbanizing streams

Stream biota in urban and suburban settings are thought to be impaired by altered hydrology; however, it is unknown what aspects of the hydrograph alter fish assemblage structure and which fishes are most vulnerable to hydrologic alterations in small streams. We quantified hydrologic variables and fish assemblages in 30 small streams and their subcatchments (area 8–20 km2) in the Etowah River Catchment (Georgia, USA). We stratified streams and their subcatchments into 3 landcover categories based on imperviousness (<10%, 10–20%, >20% of subcatchment), and then estimated the degree of hydrologic alteration based on synoptic measurements of baseflow yield. We derived hydrologic variables from stage gauges at each study site for 1 y (January 2003–2004). Increased imperviousness was positively correlated with the frequency of storm events and rates of the rising and falling limb of the hydrograph (i.e., storm “flashiness”) during most seasons. Increased duration of low flows associated with imperviousness only occurred during the autumn low-flow period, and this measure corresponded with increased richness of lentic tolerant species. Altered storm flows in summer and autumn were related to decreased richness of endemic, cosmopolitan, and sensitive fish species, and decreased abundance of lentic tolerant species. Species predicted to be sensitive to urbanization, based on specific life-history or habitat requirements, also were related to stormflow variables and % fine bed sediment in riffles. Overall, hydrologic variables explained 22 to 66% of the variation in fish assemblage richness and abundance. Linkages between hydrologic alteration and fish assemblages were potentially complicated by contrasting effects of elevated flows on sediment delivery and scour, and mediating effects of high stream gradient on sediment delivery from elevated flows. However, stormwater management practices promoting natural hydrologic regimes are likely to reduce the impacts of catchment imperviousness on stream fish assemblages.

Effect of the Colorado River Diversion on Matagorda Bay Epifauna

The effect on epifauna of the Colorado River diversion, which restored river flow to Matagorda Bay, Texas, U.S.A. was assessed using three independent data sets and analytical approaches. A monitoring study conducted by the Galveston District, U.S. Corps of Engineers, revealed lower croaker and brown shrimp abundances for 3 years following the diversion compared to their abundances during 3 pre-diversion years. No changes in the abundances of white shrimp, blue crabs and spot were evident in this monitoring study. The relative distributions of these common epifaunal organisms within the eastern arm of the bay, where the redirected river-mouth empties, did not change following the diversion. Analyses of data (1982–1995) from a long-term trawl-survey programme conducted by the Texas Parks and Wildlife Department (TPWD) indicated that the catches of common epibenthic organisms in the eastern arm of the bay following the diversion were also within the range of historic variation. Species richness decreased significantly at the eastern stations where salinities were lower following the diversion. Commercial fishery landings of most species in the post-diversion period were within the range of historic variation. Oyster landings, however, were consistently low for the 4 years for which post-diversion data were available, probably because previously harvestable reefs were lost to sedimentation and burial close to the redirected river mouth. Prior to the diversion (1970–1991), oyster landings were negatively associated with the same year's maximum annual river flows and the duration of low flows (<14m3s−1) 2 years previous (r2=0·63,P<0·001). The regression results indicate that post-diversion increases in freshwater inflows during low flow periods will likely benefit oyster harvests 2 years later Increases to oyster yields may take several more years to be realized and will be contingent upon the success of harvests from the newly created oyster reefs along the northern bay arm.

Spatial and temporal variation in fish assemblage structure in the Mary River, south-eastern Queensland: the influence of habitat structure

Fish assemblages at eleven sites within the Mary River were sampled over a 15 month period by back-pack electrofishing. The study took place during a period of abnormally low flows but included two high flow events one of which approached record levels. Spatial and temporal variation in fish assemblage structure was pronounced. Spatial variation was related to position within the catchment and correlated with habitat attributes related to substrate composition and water depth. The absence of a strong effect due to water velocity was probably due to overall low water flows throughout the study period. Temporal variation at some sites, particularly headwater sites, was correlated with changes in the amount and type of cover available to fishes. Cover was significantly correlated with the mean species richness of each site. Flooding had very little effect on both fish assemblage structure and the physical structure of the habitat but resulted in substantial reduction in the amount and type of cover available to fishes. The flow regime of the Mary River was highly variable and consequently both the timing and duration of high and low flows was unpredictable.

Logging effects on streamflow: Water yield and summer low flows at Caspar Creek in northwestern California

Streamflow data for a 21‐year period were analyzed to determine the effects of selective tractor harvesting of second‐growth Douglas fir and redwood forest on the volume, timing, and duration of low flows and annual water yield in northwestern California. The flow response to logging was highly variable. Some of this variability was correlated with antecedent precipitation conditions. Statistically significant increases in streamflow were detected for both the annual period and the low‐flow season. Relative increases in water yield were greater for the summer low‐flow period than for annual flows, but these summer flow increases generally disappeared within 5 years.

A study into the low-flow characteristics of British rivers

This paper describes investigations currently being undertaken at the Institute of Hydrology into methods for predicting low flows from catchment characteristics. Different sources of errors in flow data are described which are all taken into account when selecting suitable flow records for analysis. A number of analytical techniques which incorporate both the magnitude and duration of low flows are described and some of their areas of application given. Preliminary results highlight the need for careful screening of the data, the significance of mean annual rainfall and the need for a geology index. Catchment characteristics used in the study are then outlined together with their effect on low flows. The paper is concluded by a discussion of the regression analyses to be used in developing formulae for predicting the low flow indices from catchment and climate characteristics.