Groundwater Dependent Ecosystem Assessments

Project Description

Groundwater supports a variety of ecosystems in Nevada and the Great Basin, including springs, rivers, lakes, meadows, and wetlands, as well as trees and shrubs that tap into groundwater through deep roots (called phreatophytes). Many of these groundwater dependent ecosystems (GDEs) have small footprints on the landscape, but outsize ecological, economical, and cultural importance —  they provide water storage and purification, store carbon, provide recreational and economic benefits, many of them are considered sacred to indigenous peoples, and they provide habitats to a wealth of species, including many rare and endemics species that are found only in this region. As water demands for agriculture, mining, energy development, and potable water uses continue to increase, understanding the potential impacts of groundwater withdrawals on these ecosystems can assist efforts to sustainably manage limited water resources to meet economic and livelihood, wildlife habitat, recreation and other needs. Furthermore, understanding the influence of variability in climatic conditions on groundwater dependent vegetation will enhance our ability to better tease apart effects of climate from those associated with water management.

The DRI studies highlighted below seek to enhance this understanding by assessing historical patterns of vegetation variability and trends in relation to climate and management using 35+ years of Landsat satellite imagery, climate data, groundwater levels, unmanned aircraft systems (UAS), and field surveys for selected areas across the Great Basin. Reports and all data compiled for each of these studies are available below for download.

 

CONTACT

Christine Albano, PhD
Christine.Albano@dri.edu

Blake Minor, MS
Blake.Minor@dri.edu

Justin Huntington, PhD
Justin.Huntington@dri.edu

LOCATION

Desert Research Institute
2215 Raggio Parkway
Reno, NV 89512

DIVISION

Hydrologic Sciences

map of Nevada highlighting groundwater
Photo of Grass Springs with mountain in the background

Baseline Assessment of Groundwater Dependent Vegetation in relation to Climate and Groundwater Levels in select Hydrographic Basins of Nevada 

Objective:  To establish a baseline for monitoring and assessing the potential impacts of groundwater developments on GDEs in selected hydrographic basins of Nevada by quantifying the current status and historical trends in the condition of groundwater dependent vegetation relative to trends in both climate and groundwater levels. Analyses were completed for Pueblo, Continental Lake, Mud Meadow, Dixie, Railroad-North, Steptoe, Goshute, and Independence Valleys in Nevada. 

Key Findings: 

  • In several valleys, the areal extents of groundwater dependent vegetation (phreatophyte areas) were substantially smaller than was estimated historically, suggesting that either the historical extents were overestimated or that there have been substantial losses of groundwater dependent species due to lowered groundwater levels. These differences are important and merit further investigation, as real losses in groundwater dependent vegetation indicate large-scale ecological change, while historical overestimation of the phreatophyte area may suggest historical overestimation of the groundwater discharge, which has served as the basis for determining the perennial yield and groundwater appropriations for each valley.
  • Analysis of Landsat satellite data over 35 years revealed that vegetation outside the phreatophyte areas – especially forest and woodland vegetation was, on average, trending more positively than phreatophyte area vegetation, which tended to have only slightly positive to slightly negative trends. Areas classified as riparian, wetland, and low-intensity agricultural vegetation consistently had larger magnitude trends and tended to have a larger proportion of negative trends relative to dryland vegetation types. The trends observed in this study deserve careful consideration and future research to better isolate their causal factors.
  • Permitted groundwater rights are higher than the current estimated perennial yield in half of the eight basins assessed. Lack of consistent and long-term groundwater data was the most limiting factor in this study. Given the available data, over 25% of wells in each of five basins had statistically significant declines in groundwater levels. The largest declines in groundwater levels were most often observed in direct association with irrigated agriculture (up to 10’s of feet over 35 years) and mining activities (up to 100s of feet). 
  • Substantial human impacts were documented at all GDE sites that were visited in the field, but trends in vegetation over time varied from negative to neutral to positive. In most cases, there was insufficient groundwater levels data available to quantify groundwater-vegetation relations. This is an important data gap that will be essential to fill in order to understand the effects of water development on these ecosystems.

    Download the report and associated datasets here: 

    Status and Trends of Groundwater Dependent Vegetation in Relation to Climate and Shallow Groundwater in the Harney Basin, Oregon 

    Objective:  To increase understanding of relations between variations in climate, shallow groundwater, and groundwater dependent vegetation in the Harney Basin, OR. 

    Key Findings: 

    • Trend analyses of groundwater levels indicate widespread declines in groundwater levels across the basin; in most cases these declines were determined to be occurring independently of antecedent climate conditions. 
    • Substantial changes in surface water extent, vegetation vigor, and land use, indicated by the Landsat Normalized Difference Vegetation Index (NDVI), were evident over the course of the 35-year study period, with positive trends in NDVI indicating lake level declines since the mid-1980’s and subsequent encroachment by sparse vegetation as well as increases in irrigated cropland. Negative trends in vegetation vigor were most prominent in riparian and wetland vegetation types and low-intensity agricultural lands used as pasture and/or hayfields. 
    • Site-specific analyses of field survey and remote sensing data identified transitions from mesic (i.e., riparian and wetland) to dryland vegetation along the edges of Malheur Lake in response to declining lake and shallow groundwater levels since the 1980’s. Other areas where trends in vegetation were evident have limited evidence of groundwater declines and are places where non-native plant species invasions and intensive vegetation management activities such as mowing, prescribed fire, invasive plant management, and agricultural water management are likely influencing vegetation trends. 

    Download the report and associated datasets here: 

    Spatiotemporal Reconnaissance Investigation of Phreatophyte Vegetation Vigor for Selected Hydrographic Areas in Nevada 

    Objective:  Identify patterns of phreatophyte vegetation vigor change through space and time and qualitatively assess relations between these changes and variability in precipitation, evaporative demand, and depth to groundwater for selected hydrographic basins where significant declines in groundwater are known to have occurred due to pumping for irrigation. Analyses were completed for Kings River, Quinn River (Orovada subarea), Upper Reese River, Paradise, Grass, and Edwards Creek Valleys in Nevada. 

    Key results: 

    • Findings from this study illustrate that phreatophyte vegetation vigor changes can be observed from Landsat satellite imagery and confirmed with field investigations. 
    • Groundwater levels have substantially declined over the last 50 years in many basins, and vegetation species have become less mesic from historical observations made in the 1960s and reported in USGS Reconnaissance Series Reports 
    • An important conclusion from this study is that while declines in vegetation vigor and localized stress and mortality was observed in areas with declining water levels, facultative phreatophyte vegetation such as greasewood persists where groundwater levels were historically at or near land surface (i.e., 0 to 30 ft) and currently exceed the typically reported range of rooting depths (~20 to 60 ft) for this species, suggesting that precipitation has been sufficient to sustain these vegetation communities over the long term. 

    Download the report and associated datasets here: