Inyo County Water Department monitors vegetation conditions on the floor of the Owens Valley each year to evaluate compliance with the Long-Term Water Agreement (Agreement). The primary goal of this monitoring is to detect changes in vegetation compared to conditions recorded during the baseline vegetation mapping period (1985-1987). Baseline refers to a valley-wide inventory of vegetation cover and species composition on over 2,000 LA-owned vegetation parcels in Owens Valley, CA. The interactive map below shows the parcel boundaries in Owens Valley and clicking any polygon will provide a limited list of attribute information.
Five vegetation management types were classified based on parcel-scale evapotranspiration (ET) estimates derived from species-level leaf porometer measurements scaled up to the parcel using baseline vegetation cover and composition data. Parcels in which ET was equivalent to annual precipitation were classified as Type A. Parcels in which ET exceeded annual precipitation were classified as groundwater-dependent meadow or shrubland (Types C and B respectively), riparian/marsh (type D) and irrigated lands (type E).
|Type||Groundwater dependent||Irrigation dependent||Evapotranspiration (ET)|
|B||yes||no||ET > Precipitation|
|C||yes||no||ET > Precipitation|
|D||yes||no||ET > Precipitation|
Transition of any parcel to a groundwater and vegetation condition that precedes it alphabetically is contrary to the goals of the Agreement. The depth of the water table below ground surface constrains the spatial distribution of groundwater-dependent ecosystems (GDEs) in Owens Valley and is critical to groundwater-dependent vegetation management under the Agreement.
Transects for monitoring vegetation response to pumping
The line-point-intercept method is used to provide estimates of live vegetation cover in parcels potentially influenced by groundwater extraction and these data are used to statistically compare cover and composition to baseline data each year. This reinventory method was adopted by the Inyo-LA technical group for compliance monitoring and has been ongoing since 1991. In 2017, Green Book Box I.C.l.a.ii was updated to reflect the most recent methods used by ICWD and LADWP in this joint monitoring program.
TRANSECTS FOR MONITORING VEGETATION RESPONSE TO PUMPING
Vegetation transects are included within the Green Book to serve two purposes: 1) to estimate transpiration from a monitoring site, and 2) for use in determining whether vegetation has decreased or changed significantly from the previous cover.
- Detailed measurements of leaf area index shall be made at each of the monitoring sites using the techniques described in Section III.C. These measurements will be used to estimate evapotranspiration from the vegetation at the monitoring site for comparison to available soil water and, ultimately, to project plant-soil water balance and the need for water table recovery. Vegetation transects shall also be used in cases of suspected vegetation changes due to groundwater pumping. However, rather than using the intensive sampling technique of Section III.D for calculating evapotranspiration, plant cover shall be measured by the line-point technique described below.
- During the 1984-87 inventory, most parcels were sampled with line-point transects of 100 feet in length, with sampling points at one-foot intervals, providing a two-dimensional representation of vegetation within the parcel. At each one-foot marker, the first contact with the uppermost layer of live plant cover was recorded. Cover and species composition were calculated from all sampling points along the transect.
The 1984-87 inventory shall be used as a “baseline” to determine whether vegetation cover and/or species composition has changed. This inventory is the only one of sufficient accuracy to permit comparison of species composition and cover.
A subset of the vegetation parcels mapped during the 1984-87 baseline inventory shall be annually monitored to accommodate statistical comparison with data collected during the baseline inventory. Such monitoring may rely on repeat measurement of georeferenced locations using the line-point-intercept method to track live cover and species composition over time. The baseline inventory was summarized at the parcel scale, thus for statistical comparison, transect locations derived from a set of random locations and azimuths provide a valid statistical comparison.
Parcels to be monitored were initially selected based on meeting one or more of the following criteria: (1) parcel contained a permanent monitoring site; (2) baseline inventory data were collected for the parcel; (3) parcel was in close proximity to a pumping well; (4) information of past and current land use for parcel was available; (5) parcel was representative of one of the groundwater-dependent plant communities originally mapped during the baseline inventory; (6) soil characterization was available for the parcel; (7) characterization of the landscape position was available for the parcel. In 2015, Inyo County and Los Angeles began a joint monitoring program utilizing a combination of parcels and transects evaluated and agreed upon by the staffs of both parties. As of 2016, 1,688 transects across 141 parcels are jointly monitored by both parties.
Approximately 100 of the 141 parcels monitored in 2016 will be jointly selected and monitored each year by Inyo County and Los Angeles. Prior to the field season, staff from both parties will determine which parcels of the 141 will be monitored. Existing permanent transects will be used for those parcels selected unless the staffs of both parties agree that a change in transect location is justified and necessary. Transects will be evenly split between ICWD and LADWP. Either party may independently conduct monitoring of additional parcels or transects; however, any data so collected shall be provided to the other party.
The field protocol and calibration for field observations for the joint line-point monitoring program largely follows Herrick et al.(2016). At the onset of the monitoring season, staff from both parties shall meet in the field to discuss methods and to calibrate all field personnel. In summary the field protocol is as follows:
- navigate to the transect start point with a handheld GPS device;
- verify presence of an aluminum tag which has been previously attached to a nearby object (i.e. shrub, debris, etc.);
- use a photo taken from the previous year to precisely locate the transect start point and to examine the accuracy of the azimuth used during the previous year;
- if the start point on the photo is off by more than 6 meters from the point indicated by a GPS reading, or a start point cannot be positively identified, a start point will be placed at the point indicated by the GPS device;
- if the designated transect azimuth is off by more than ±5 degrees from the azimuth depicted within the previous year’s transect photo, the designated transect azimuth will be used. If not, the azimuth depicted within the previous year’s photo will be upheld;
- stretch a tape measure to the direction of the pre-established azimuth;
- for each transect, notes shall be taken on whether an aluminum tag is present, and whether or not the current year’s start point and compass azimuth matches those depicted within the previous year’s transect photo;
- record species identity at each half meter starting at 0.5 m and ending at 50 m yielding 100 possible hits;
- place a dry erase board with the parcel name, transect number, azimuth and date at the base on the transect line and take a picture from the start point toward the end point that captures the entire transect.
All live cover is tallied for each species for each transect. Data are exchanged at the end of the field season after each party digitally enters and proofs field data.
The field technique and sampling design may be modified to permit detailed statistical comparison if deemed necessary in the future. Statistical analysis will be used to determine the measurability (statistical significance) of vegetation changes from the 1984-87 baseline inventory maps. Such an analysis may include, but is not limited to, Welch’s test (t-test with unequal variance), Wilcox test (Mann-Whitney test), Analysis of Variance (ANOVA) and Generalized Linear Model (GLM) for vegetation cover and permutational Multivariate Analysis of Variance (PERMANOVA) and Nonmetric Multidimensional Scaling (NMDS) for vegetation composition. For parcels with small baseline inventory sample sizes (e.g. 1-4 transects), a one-sample t-test may be performed using the baseline inventory sample mean as the null hypothesis for the test. Determination of measurability will be made by the Technical Group on case by case basis in accordance with Water Agreement IV.B and Green Book Section I.C.
Box I.C.1.a.ii shall be modified as necessary in the future to incorporate new or modified field techniques, technology, and/or analytical methods. Such changes will be jointly developed by the staffs from both Inyo County and Los Angeles and will be presented to the Technical Group for consideration.
The Welch-Satterthwaite t-test is used to test for significant differences from baseline in total perennial vegetation cover and perennial grass cover separately at the 0.05 level. In the following maps, parcels colored red denote below baseline conditions.
Below are tabulated groundwater-dependent parcels monitored in 2017 in well fields and control areas sorted north to south. Total perennial cover (TPC) and perennial grass cover (PGR) were compared to baseline data using a two-sample t-test or one sample t-test depending on baseline sample size. Statistically significant declines from baseline (Δ TPC, Δ PGR ) are shown as filled black circles; no change and increases since baseline are shown with open circles. Well field and control designations and Green Book vegetation yype is shown for reference. Well field parcels below baseline perennial cover are highlighted in red. Control parcels below baseline are highlighted in blue.
Individual Parcel Time Series
All reinventoried parcels
2017 Time series – all reinventoried parcels
Wellfield parcels below baseline
2017 Time series – well-field parcels below baseline