Perennial Streams Research Articles

Sediment and Phosphorus Inputs from Perennial Streams to Lake Whatcom, Washington State

Relationships among suspended sediment, phosphorus, and discharge vary temporally and spatially in the Lake Whatcom watershed, a 125-km 2 , high-relief, moderately developed, forested basin in northwestern Washington State. The lake is subject to a Total Maximum Daily Load to limit phosphorus inputs. Phosphorus, which largely enters the lake adsorbed to suspended sediment in streams, has led to increased algae growth and depletion of dissolved oxygen. We used the results of high-resolution storm event sediment and phosphorous sampling in five streams to examine the effects of varying watershed features on loading and to develop sediment-discharge and phosphorus-discharge models to estimate phosphorus loading to the lake during the 2013 water year. During most storm events, the sediment peak preceded the discharge peak. The magnitude of hydrograph rise was the best predictor of the maximum sediment concentration during the event. Of the five basins studied, a large, forested watershed that contains steep slopes susceptible to mass wasting yielded the most sediment per area. The highest phosphorus yield was from a smaller, lower-relief watershed containing 29 percent residential development. Our sediment and phosphorous yields were comparable to estimates from similar streams in the Puget Sound region in northwest Washington State. Total suspended solids and total phosphorus were significantly correlated to discharge in most streams in the watershed, but variability within and among storm events resulted in uncertainty when calculating fluxes based on discharge.

Macroinvertebrate community responses to hydrological controls and groundwater abstraction effects across intermittent and perennial headwater streams

Intermittent rivers comprise a significant proportion of river networks globally and their spatial extent is predicted to increase with rising water abstraction pressures. Despite this, the ecological implications of hydrological modifications within intermittent rivers have received limited research attention. This paper examines macroinvertebrate assemblages across intermittent and perennial sections of headwater streams within the Hampshire Avon catchment (United Kingdom) over a five-year period. The composition of faunal assemblages was quantified in relation to four hydrological metrics: the duration of flowing conditions, the geographical proximity to the nearest perennial source along each watercourse (two observed flow parameters) and two modelled groundwater abstraction influences. The results highlight that macroinvertebrate communities inhabiting sites which dry periodically and are positioned at greater distances (>c. 2.5km) above the perennial source (the most upstream point of permanent flow within a given year) possessed the highest conservation values. These sites supported species that are rare in many areas of Europe (e.g. Ephemeroptera: Paraletophlebia werneri) or with limited geographical distribution across the United Kingdom (e.g. Trichoptera: Limnephilus bipunctatus). A range of faunal community diversity indices were found to be more sensitive to the antecedent flow duration and distance from the perennial source, rather than any effects of groundwater abstraction. Taxonomic richness responded most strongly to these observed flow parameters and varied more markedly with the distance from the perennial source compared to the antecedent flow duration. Several taxa were significantly associated with the observed flow parameters, particularly those predominantly inhabiting perennially flowing systems. However, the distance that such fauna could migrate into intermittent reaches varied between taxa. This research demonstrates the overriding importance of antecedent flow durations and the geographical proximity to perennial sources on macroinvertebrate communities within intermittent and perennial headwater streams.

Palaeokarst Deposits in Caves: Examples from Eastern Australia and Central Europe

Palaeokarst deposits are most commonly found in excavations, drill holes and naturally exposed at the Earth’s surface. Some caves however intersect palaeokarst deposits. This occurs in large hypogene caves in the USA, thermal caves in Hungary and in many caves in eastern Australia. Palaeokarst deposits in caves respond to cave forming processes in the same way as hostrock: the palaeokarst deposits form cave walls. A range of palaeokarst deposits is exposed in caves including; filled tubes, walls composed of flowstone, large-scale bodies, breccia pipes, dykes, volcaniclastic palaeokarst and crystalline palaeokarst. As well as being exposed in cave walls, palaeokarst deposits can wholly or partly form speleogens (speleogens made from palaeokarst). Records of geological events not preserved elsewhere can occur in palaeokarst deposits in caves. These can be difficult to correlate with conventional geological histories. It is important to be able to distinguish between palaeokarst deposits, relict sediments and phantom rock (in-situ weathered rock, also called ghost rock; Vergari & Quinif 1997). Relict sediments can be distinguished from palaeokarst deposits because the cave walls bound relict sediments while palaeokarst deposits form the cave walls. Palaeokarst can be distinguished from phantom rock, as palaeokarst is unconformable with the hostrock, with structures in the hostrock not continuing across the boundary into the palaeokarst. Hostrock structures and textures do continue across the boundary between unaltered hostrock and phantom rock. Similarly, cave sediments are unconformable or disconformable with the hostrock while phantom rock is conformable with hostrock containing hostrock structures and textures. It has been difficult to explain why palaeokarst occurs in some caves and not others. One explanation worth considering is that palaeokarst deposits are not intersected by caves or sections of caves that contain large perennial streams and/or have undergone large-scale vadose fluvial development capable of escaping from the bounds of structural guidance, such as the caves in the Classical Karst. Key words: palaeokarst, caves, Australia, relict sediments, phantom rock.

Streamflow-base flow ratio in a lowland area of North-Eastern Romania

The ratio between streamflow and base flow for 3 catchments from lowland area of North-Eastern Romania were calculated with six different separation methods: the local minimum method, Talaksen filter, Chapman filter, recursive digital filter, WHAT model, and the Ekchardt filter. In agreement with an increase in precipitation levels in the past decades all filter-based methods indicate a slight increase in Base Flow Index (BFI) values throughout the study period (1981–2013). The Eckhardt filter associated with Chapman filter are the most appropriate methods to evaluate the ratio between streamflow and base flow for this area. Both methods suggest the identification of parameters a and BFImax (a = 0.925, BFImax = 0.5–0.7). Taking into account the highly variable hydrological regime throughout the year, and the fact that 35% of the hydrographic network displays ephemeral stream, the values obtained for the BFI based on these algorithms are the following: BFI = 0.58 for basins developed on porous aquifers with perennial stream (asuming a = 925 and BFImax = 0.7) and BFI = 0.52 for basins developed on porous aquifers, but with ephemeral stream (asuming a = 925 and BFImax = 0.5).

On the probability distribution of daily streamflow in the United States

Abstract. Daily streamflows are often represented by flow duration curves (FDCs), which illustrate the frequency with which flows are equaled or exceeded. FDCs have had broad applications across both operational and research hydrology for decades; however, modeling FDCs has proven elusive. Daily streamflow is a complex time series with flow values ranging over many orders of magnitude. The identification of a probability distribution that can approximate daily streamflow would improve understanding of the behavior of daily flows and the ability to estimate FDCs at ungaged river locations. Comparisons of modeled and empirical FDCs at nearly 400 unregulated, perennial streams illustrate that the four-parameter kappa distribution provides a very good representation of daily streamflow across the majority of physiographic regions in the conterminous United States (US). Further, for some regions of the US, the three-parameter generalized Pareto and lognormal distributions also provide a good approximation to FDCs. Similar results are found for the period of record FDCs, representing the long-term hydrologic regime at a site, and median annual FDCs, representing the behavior of flows in a typical year.

Long-Term Quantification of Stream-Aquifer Exchange in a Variably-Saturated Heterogeneous Environment

A variably-saturated finite element model HYDRUS-2D was used to simulate the spatiotemporal dynamics of stream-aquifer exchange for a perennial stream flowing through an undulating catchment and underlain by heterogeneous geology. The model was first calibrated and validated using piezometric heads measured near the stream. The model was then used a) to quantify the long-term dynamics of exchange at stream-aquifer interface and the water balance in the domain, and b) to evaluate the impact of anisotropy of geological materials, thickness (w) and hydraulic conductivity (K s ) of the low permeability layer at the streambed, and water table fluctuations on the extent of exchange. Simulated pressure heads in the domain revealed that seasonal groundwater fluctuations were more pronounced near the stream. Daily discharge to the stream varied from 0.05 to 0.3 mm/day, annual discharge ranged from 59 to 74 mm, and the overall water balance showed a discharge (−54 mm) from the domain during 2000–2012. A five-fold increase in K s of the low permeability layer enhanced discharge to the stream by 14% (10 mm/year) whereas an increase in the thickness of the layer by 1 m had a low impact (2.4 mm/year). A 2-m drawdown of the water table transformed a connected and gaining system into a losing, disconnected system. These results suggest that depletion of groundwater due to climate change or excessive pumping could have a pronounced impact on the availability of water resources and sustainability of the existing water-dependent ecosystem.

The geomorphic impacts of culverts at paved forest roads: Examples from Carpathian headwater channels, Czech Republic

Road-stream crossings constructed with culverts have the potential to alter geomorphic processes in adjacent stream channels. We examined changes in channel geometry and bed sediments in longitudinal profiles related to culverts at five paved forest road crossings with perennial headwater streams and two gullies initiated by point releases of water through ditches. A dendrogeomorphic approach was used for dating of exposed tree roots and estimation of bank erosion rates in incised cross-sections downstream of road crossings. The studied forest road crossings concentrate surface runoff from the road net, act as stabilizing elements in stream longitudinal profiles and decelerate bedload transport in the case of culvert clogging, which caused notable upstream and downstream changes in fluvial processes. Notable fining of the coarsest fraction in upstream cross-sections was observed only for two culverts with the highest depositional tendencies. Much lower width-depth ratios (<4) and typically higher channel slopes were measured in channel reaches downstream of the culverts, compared with upstream cross-sections. Two road-induced gullies typically had very low width/depth ratios close to 2. At five of a total of seven studied culverts, the highest documented erosion rates occurred immediately downstream of these structures. The mean annual erosion rates reconstructed from cross-sections at the positions of individual tree root samples ranged from 0.2 to 6.5cm·year−1, and the erosion occurred over 2–5year intervals, depending on the studied location. The highest number of observed changes in cross-sectional geometry caused by channel erosion were connected with relatively high-magnitude flow events (with recurrence intervals >10years; specific discharge >1500l·s·km−2), whereas more frequent flows (with recurrence intervals of 2–10years) were not always recorded by exposed tree roots.

Riparian plant composition along hydrologic gradients in a dryland river basin and implications for a warming climate

AbstractDroughts in dryland regions on all continents are expected to increase in severity and duration under future climate projections. In dryland regions, it is likely that minimum streamflow will decrease with some perennial streams shifting to intermittent flow under climate‐driven changes in precipitation and runoff and increases in temperature. Decreasing base flow and shifting flow regimes from perennial to intermittent could have significant implications for stream‐dependent biota, including riparian vegetation. In this study, we asked, how do riparian plant communities vary along wet‐to‐dry hydrologic gradients on small (first–third order) streams? We collected data on geomorphic, hydrologic, and plant community characteristics on 54 stream sites ranging in hydrology from intermittent to perennial flow across the Upper Colorado River Basin (284,898 km2). We found that plant communities varied along hydrologic gradients from high to low elevation between streams, and perennial to intermittent flow. We identified indicator species associated with different hydrologic conditions and suggest how plant communities may shift under warmer, drier conditions. Our results indicate that species richness and cover of total, perennial, wetland, and native plant groups will decrease while annual plants will increase under drying conditions. Understanding how plant communities respond to regional drivers such as hydroclimate requires broad‐scale approaches such as sampling across whole river basins. With increasingly arid conditions in many regions of the globe, understanding plant community shifts is key to understanding the future of riparian ecosystems.

Structural and functional recovery of macroinvertebrate communities and leaf litter decomposition after a marked drought: Does vegetation type matter?

Climate change and anthropogenic disturbances are expected to lead to more intense and frequent droughts, with potentially severe effects on structure and function of perennial temperate streams. However, more information is required on whether streams flowing through basins already affected by exotic plantations will respond to droughts in the same way as streams under native forests. The recolonisation dynamics of benthic macroinvertebrate communities and leaf litter decomposition rates were examined in nine streams of oceanic-temperate climate that differed in catchment vegetation (three streams draining native deciduous forest, three in pine plantations and three in eucalypt plantations) after a marked drought. In each stream, five benthic samples were collected three times (ca. 1.5months between sampling dates) after flow recovery, and the taxonomic and functional trait compositions of the macroinvertebrate communities were analysed. The decomposition rate of Alnus glutinosa was measured in fine- and coarse-mesh litter bags. Benthic macroinvertebrate density, richness and diversity increased with time after flow recovery but only richness and diversity differed among stream types, with eucalypt streams showing the lowest values. Both the taxonomic and functional compositions of the macroinvertebrate community were dependent on vegetation type and time, with the differences among stream types diminishing over time. While leaf-litter decomposition rate did not depend on catchment vegetation after drought, detritivore activity was the lowest under eucalypt streams and it was positively correlated to benthic shredder density. Our results indicated that in these perennial temperate streams the catchment vegetation influenced the recovery of benthic macroinvertebrate communities after a period of drought, although the decomposition rate of leaf litter was not strongly affected. Greater understanding of the structural and functional responses of stream ecosystems to different stressors is required before the effects of expected more intense and frequent hydrological changes caused by climate change can be adequately forecast.

Importance of neutral processes varies in time and space: Evidence from dryland stream ecosystems.

Many ecosystems experience strong temporal variability in environmental conditions; yet, a clear picture of how niche and neutral processes operate to determine community assembly in temporally variable systems remains elusive. In this study, we constructed neutral metacommunity models to assess the relative importance of neutral processes in a spatially and temporally variable ecosystem. We analyzed macroinvertebrate community data spanning multiple seasons and years from 20 sites in a Sonoran Desert river network in Arizona. The model goodness-of-fit was used to infer the importance of neutral processes. Averaging over eight stream flow conditions across three years, we found that neutral processes were more important in perennial streams than in non-perennial streams (intermittent and ephemeral streams). Averaging across perennial and non-perennial streams, we found that neutral processes were more important during very high flow and in low flow periods; whereas, at very low flows, the relative importance of neutral processes varied greatly. These findings were robust to the choice of model parameter values. Our study suggested that the net effect of disturbance on the relative importance of niche and neutral processes in community assembly varies non-monotonically with the severity of disturbance. In contrast to the prevailing view that disturbance promotes niche processes, we found that neutral processes could become more important when the severity of disturbance is beyond a certain threshold such that all organisms are adversely affected regardless of their biological traits and strategies.

A comparative analysis on the effects of river discharge on trophic interactions in two tropical streams

Discharge-mediated seasonal patterns of food web interactions were investigated in two streams in Sri Lanka; Eswathu Oya (a perennial wet-zone stream) and Yan Oya (a seasonal dry-zone stream). Based on volumetric proportions of diet composition, relative abundance of fish species and their daily food rations, the mean cumulative consumption of each prey taxon was estimated for each fish population. Food web diagrams were prepared using trophic index of fish, trophic class of prey and feeding interactions between fish and prey. Both streams showed seasonal patterns of discharge due to rainfall, but no significant effect was evident in the trophic index of most fish species. In both streams, cumulative consumption of prey taxa was highest during low discharge regime due to increased abundance of both prey taxa and consumers. In Eswathu Oya, diversity of prey taxa was higher during the low discharge regime, but in Yan Oya, high diversity occurred during the high discharge regime. Herbivorous and/or detritivorous fish species were rare in Eswathu Oya but dominant in Yan Oya. Complex food web structure in Yan Oya due to high fish species richness and high diversity of prey categories made it less sensitive to discharge extremes in contrast to relatively simple food web structure in Eswathu Oya. This study, therefore, highlights the importance of maintaining the quality of riparian environments for conservation of biodiversity.

Landscape- and local-scale habitat influences on occupancy and detection probability of stream-dwelling crayfish: implications for conservation

Crayfish are ecologically important in freshwater systems worldwide and are imperiled in North America and globally. We sought to examine landscape- to local-scale environmental variables related to occupancy and detection probability of a suite of stream-dwelling crayfish species. We used a quantitative kickseine method to sample crayfish presence at 102 perennial stream sites with eight surveys per site. We modeled occupancy (psi) and detection probability (P) and local- and landscape-scale environmental covariates. We developed a set of a priori candidate models for each species and ranked models using (Q)AICc. Detection probabilities and occupancy estimates differed among crayfish species with Orconectes eupunctus, O. marchandi, and Cambarus hubbsi being relatively rare (psi 0.60) with high detection probability (0.81). Detection probability was often related to local habitat variables current velocity, depth, or substrate size. Important environmental variables for crayfish occupancy were species dependent but were mainly landscape variables such as stream order, geology, slope, topography, and land use. Landscape variables strongly influenced crayfish occupancy and should be considered in future studies and conservation plans.

Distribution and habitats of &lt;i&gt;Burnupia trapezoidea&lt;/i&gt; (Boettger, 1910) (Gastropoda: Ancylidae) in South Africa

This paper deals with the geographical distribution and habitat preferences of B. trapezoidea , the third most widespread species of the 14 species of Burnupia currently on record in the database of the National Freshwater Snail Collection (NFSC) of South Africa. Although the 121 loci ( 1 / 16 square degrees) from which the 445 samples of B. trapezoidea were collected are much fewer than the number reported for B. capensis , the range of its geographical distribution is almost as widespread as that of B. capensis . The limited distribution of B. trapezoidea in the Limpopo, Northern Cape and Western Cape Provinces can most probably be attributed to the paucity of perennial water bodies in these areas and the fact that Burnupia spp. in general have poor abilities to overcome conditions of desiccation prevalent in these areas. It is therefore not surprising that the majority of samples were collected in perennial rivers and streams. A Random Forest statistical analysis selected water bodies, the presence or absence of marginal and aquatic vegetation, and type of substratum as the most important variables that played a significant role in determining the presence and numbers of specimens of B. trapezoidea in a specific area. In this respect, temperature and turbidity, respectively, played a moderate and minor role. Little is known regarding the conservation status of Burnupia spp, in general, but habitat degradation and climatic warming could be reasons for concern. However, in extensive on-going biodiversity surveys in two rivers and selected tributaries in the North-West Province, many new distribution records of B. trapezoidea are still being created and therefore this species could probably be considered for listing as not endangered. In view of its wide distribution, largely sessile, benthic lifestyle, and ability to bioaccumulate various substances, the feasibility to utilise it as indicator of river ecosystem health in South Africa should be explored. Keywords: Mollusca, Ancylidae, Burnupia trapezoidea , geographical distribution, habitat preferences, conservation status, South Africa

A geomorphic assessment to inform strategic stream restoration planning in the Middle Fork John Day Watershed, Oregon, USA

ABSTRACTA geomorphic assessment of the Middle Fork John Day Watershed, Oregon, USA, was used to generate a hierarchical, map-based understanding of watershed impairments and potential opportunities for improvements. Specifically, we (1) assessed river diversity (character and behavior) and patterns of reach types (and their controls); (2) evaluated the geomorphic condition of the streams; (3) interpreted their geomorphic recovery potential; and (4) synthesized the above into a hypothetical, strategic management plan. Collectively, these maps can set bounds and provide realistic guidance for river rehabilitation, design and implementation efforts. Fifteen distinct reach types were identified, two-thirds of which are found along perennial streams. On the basis of a variety of geo-indicators, approximately two-thirds of all perennial stream reaches were found to be in ‘good’ geomorphic condition, whereas one-third had departed to ‘moderate’ and ‘poor’ condition. Departures from ‘good’ condition were primarily related to riparian vegetation removal, conversion of floodplain to agricultural land uses (farming and grazing), logging, and channel bed dredge mining for gold. Encouragingly, the majority of reaches classified as being in moderate geomorphic condition were found to have high recovery potential. While our geomorphic assessment has practical utility for informing physically realistic expectation management for efforts like salmonid habitat restoration, the maps themselves are the key vehicle for communicating and visualizing among stakeholders.

Combining observations of channel network contraction and spatial discharge variation to inform spatial controls on baseflow in Birch Creek, Catskill Mountains, USA

Study regionThis study was carried out in the 32km2 Birch Creek watershed in the Catskill Mountains of New York State. Birch Creek is situated within the Hudson River Basin. Study focusVery few studies have paired measurements of changes in the extent of the actively flowing channel network with measurements of small scale flow variations. In this study, we map changes in a 23.5km active channel network and concurrently take periodic measurements of discharge at 31 sub-channels (with drainage areas ranging from 0.04 to 11.5km2) in order to better understand the spatial distribution of baseflow generation over time within the catchment. New hydrological insightsFor the 31 different sub-channels, baseflow discharge per unit drainage area and per unit stream length were highly variable, even during periods of higher moisture storage when all channels were active. Simple mapping of the active channels would not have recognized these sizable spatial differences in discharge contribution. Previous studies of hydrologic scaling in the Catskills have noted the likelihood of heterogeneity in discharge below a threshold of approximately 3–8km2. This study provides direct documentation of such heterogeneity at smaller spatial scales. When considering perennial and ephemeral streams, such heterogeneity was not well explained by standard topographic, geologic, or meteorological factors. We suggest the heterogeneity may arise from difficult to map fine-scale variations in subsurface properties.

Legal ecotones: A comparative analysis of riparian policy protection in the Oregon Coast Range, USA

Waterways of the USA are protected under the public trust doctrine, placing responsibility on the state to safeguard public resources for the benefit of current and future generations. This responsibility has led to the development of management standards for lands adjacent to streams. In the state of Oregon, policy protection for riparian areas varies by ownership (e.g., federal, state, or private), land use (e.g., forest, agriculture, rural residential, or urban) and stream attributes, creating varying standards for riparian land-management practices along the stream corridor. Here, we compare state and federal riparian land-management standards in four major policies that apply to private and public lands in the Oregon Coast Range. We use a standard template to categorize elements of policy protection: (1) the regulatory approach, (2) policy goals, (3) stream attributes, and (4) management standards. All four policies have similar goals for achieving water-quality standards, but differ in their regulatory approach. Plans for agricultural lands rely on outcome-based standards to treat pollution, in contrast with the prescriptive policy approaches for federal, state, and private forest lands, which set specific standards with the intent of preventing pollution. Policies also differ regarding the stream attributes considered when specifying management standards. Across all policies, 25 categories of unique standards are identified. Buffer widths vary from 0 to ∼152 m, with no buffer requirements for streams in agricultural areas or small, non-fish-bearing, seasonal streams on private forest land; narrow buffer requirements for small, non-fish-bearing perennial streams on private forest land (3 m); and the widest buffer requirements for fish-bearing streams on federal land (two site-potential tree-heights, up to an estimated 152 m). Results provide insight into how ecosystem concerns are addressed by variable policy approaches in multi-ownership landscapes, an important consideration to recovery-planning efforts for threatened species.

Hydrology drives seasonal variation in dryland stream macroinvertebrate communities

Many lotic ecosystems are spatially and temporally heterogeneous but none more so than dryland streams flowing through arid and semi-arid landscapes. Understanding seasonal variation in richness and trait composition is critical to our fundamental understanding of these dynamic stream networks. Here, we analyzed aquatic macroinvertebrate communities within perennial and intermittent reaches in replicate dryland watersheds in southwestern USA across 10 seasons and 4 years. We quantified how hydrology, season, and microhabitat type affected taxa richness and trait composition. Taxa richness was higher in perennial than intermittent reaches, in pools than riffles, and in fall and summer than in spring. The interaction between hydrology and season was important; the difference between fall high and spring low richness was greater in intermittent than perennial streams. Hydrology was the main predictor of trait composition; intermittent streams supported a larger fraction of small taxa, taxa with the ability to undergo diapause, and uni- or multivoltine taxa (i.e., taxa with shorter life cycles). Trait composition did not vary across seasons among perennial reaches whereas the fraction of aerial dispersers appeared to be greater in spring than other seasons among intermittent reaches. Our results were largely consistent with predictions of the habitat templet; r-selected traits were more frequently represented in intermittent communities. The temporal characterization of macroinvertebrate community structure in dryland streams provides a powerful glimpse of how stream communities may respond to a drying climate.

Reduced Gene Flow in Two Common Headwater Fishes in the Ouachita Mountains: A Response to Stream Drying and In-stream Barriers

Stream drying and in-stream barriers can influence migration and recolonization, yet we know little about how these impact population genetics of fishes. We analyzed microsatellite DNA from two common headwater fishes, Longear Sunfish (Lepomis megalotis) and Highland Stoneroller (Campostoma spadiceum), to compare population genetics of fishes in streams with varying degrees of connectivity. We sampled perennial and intermittent streams including examples with and without anthropogenic structures (road crossings). An additional perennial stream with a large waterfall was added to examine potential effects of a natural structure. We collected between 24 and 30 individuals of each species from three equidistant locations along each of five study streams. We found that Longear Sunfish and Highland Stoneroller populations experienced greater reductions in gene flow along the intermittent streams than along the perennial streams. However, the greatest reduction in gene flow between sub-populations generally coi...

Geochemical, economic, and ethnographic approaches to the evaluation of soil, salinity, and water management in Chaco Canyon, New Mexico

Salinity meter, powder X-ray diffraction, inductively coupled plasma atomic emission spectroscopy, and energy dispersive X-ray fluorescence spectrometry of alluvium and anthropogenic sediments demonstrates that the salinity levels of the water and soil resources used by Ancestral Puebloan people during the Bonito Phase in Chaco Canyon, New Mexico were negligible. Salinity levels were not high enough to argue that they were deleterious to farming at Chaco Canyon. The overtly high salinity levels reported by Benson cannot be replicated. Ethnographic data show that Chaco Canyon contained more than adequate sediments (perennial stream alluvium, ephemeral rincon alluvium, aeolian sand dunes) needed to support the maize-based economy of a large Ancestral Puebloan population. The occurrence of cultigens from the Chuska Slope can be explained in terms of the economic processes of production, distribution, and exchange of goods and services that originated, sustained, enhanced, or reproduced the livelihood of Ancestral Puebloans.

Environmental flows in the desert rivers of the United States and Mexico: Synthesis of available data and gap analysis

Although riparian and aquatic ecosystems make up a small fraction of the area in arid and semi-arid lands, they are critical for the survival of desert life. There are, however, few compendia of efforts to define the quantity of water needed to maintain these ecosystems and understand the risks and stressors to them. Through our analysis we found that 62% of the rivers examined in the deserts of the U.S. and Mexico have had just one study over the past four decades and 67% of studies used qualitative methods. Furthermore, only one-third of the 312 species catalogued in our work have been studied more than once and only 5% have been considered five or more times. The most common risks or stressors to riparian and aquatic species were engineered structures, invasive species, and altered flows; and while 10% of studies included climate stressor, climate change impacts were infrequently examined. Ultimately, we found that although research has been conducted across the desert watersheds of the U.S. and Mexico, there are significant gaps in our knowledge of basic data such as the location and extent of perennial and intermittent streams, let alone studies of environmental flow needs.