The Water Department monitors groundwater-dependent vegetation on the floor of the Owens Valley to evaluate Long-Term Water Agreement vegetation management goals.
|Type||Groundwater dependent||Irrigation dependent||Evapotranspiration (ET)|
|B||yes||no||ET > Precipitation|
|C||yes||no||ET > Precipitation|
|D||yes||no||ET > Precipitation|
|E||no||yes||ET > Precipitation|
BOX I.C.l.a.ii 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.