Abstract
California is under a state of emergency
because of the prolonged drought that it is currently experiencing. Moreover,
greater than 80 % of the water consumed in the state of California is
attributed to farming purposes (Porvair, 2015). This has put the entire country
on alert, since California produces nearly half of the fruits, vegetables, and
nuts grown in the United States. The drought is already causing dramatic
economic impacts both state- and nationwide. However, there are additional implications
that have received less attention, such as the effect of the drought on water
quality, which will in turn, affect agriculture.
Agriculture in
California and the groundwater quality problem
California, the fruit and vegetable farm of the
United States, is feeling the effects of the lack of water (Figure 1). The
state is stepping into year four of drought and a second year of severe water
restrictions on farmers. Growers are reducing acreage and installing more
efficient irrigation systems to conserve water (Porvair, 2015), and this
situation has already started to affect the economy. Direct costs to
agriculture total $1.5 billion (revenue losses of $1 billion and $0.5 billion
in additional pumping costs). This net revenue loss is about 3 percent of the
state’s total agricultural value (Davis, 2015). Moreover, the University of
California Davis (2015) predicts that the state will likely lose 17,100
agricultural jobs because of the drought. These harsh realities imply that California’s
water scarcity is already taking its toll on consumer pocketbooks, as farmers
idle land, and drive up commodity prices. The U.S. Department of Agriculture
predicts that prices are expected to rise in 2016; fresh fruits by 1.5 to 2.5 %
and fresh vegetables by 1.0 to 2.0 % (USDA, 2015). Aside from its economic
impact, the drought has other implications that could result in additional and
prolonged repercussions on agricultural production.
During a drought, reliance upon groundwater
increases, often resulting in higher groundwater pumping to meet water demands.
California obtains approximately 30–40% of its average annual water supply from
groundwater (Carle, 2004). However, prolonged high rates of ground water
withdrawal have exceeded rates of recharge in a number of aquifers in the
southwest (Figure 2). This had led to drops in local and regional water tables
of 10 m to over 30 m in areas of southern California and adjacent states (Leake
et al., 2000).
The withdrawal of large amounts of groundwater
and the lowering of water tables have also produced considerable subsidence in
many regions. The arid Antelope Valley of southern California, for example, has
experienced 2 m of water-related subsidence in some areas since the 1940s
(Bawden et al., 2003).
As illustrated by USGS California Water Science
Center, Figure 2 depicts the groundwater levels in different parts of the Santa
Barbara-Santa Maria area in southern California, highlighting that all of the
tested points show a groundwater level below normal. If a well is pumped at a
faster rate than its aquifer is recharged by precipitation or other underground
flow, water levels in the well can drop, resulting in decreased water
availability (Figure 2) and deterioration of groundwater quality. For instance,
during dry periods, surface water (e.g. rivers, lakes, etc.) that usually
receive groundwater, might instead begin losing water to the aquifers if the
water table is low. This could cause the contaminants (salts, nitrates,
bacteria, etc.) in the surface water to flow into the aquifer, thus altering
its water quality.
Deeper water is more expensive to pump to the
surface, but this is not the only problem. In coastal regions, groundwater
pumping can cause incursions of saltwater from the Pacific Ocean into coastal
aquifers. Ocean water intrusion compromises groundwater quality and can be a
difficult and expensive problem to manage. In areas like southern California,
in the absence of adequate surface water during a long dry season, irrigation
becomes heavily dependent on groundwater. The present drought is causing
farmers to drill deeper wells, where on average we expect mineral
concentrations to be greater than those of shallower wells.
To give a specific example of the water
problem, in the Oxnard district (Ventura County) strawberry growers continue to
use available groundwater. This crop is very sensitive to salinity and frequent
irrigation is practiced to prevent the accumulation of salts in the root zone.
One downside of this practice is that growers are using even more groundwater
resources in order to allow extra irrigation to flush down salts from the root
zone, ultimately resulting in nutrient leaching and further accumulation of
salts in the already exhausted aquifers. This could lead to a reduction in
fruit yields, which would likely affect the final price of the product, thus
aggravating the economic problems derived from the drought.
In order to minimize the consequences caused by
the scarcity of water, it is critical for farmers to evaluate the chemical
suitability of their irrigation water (through laboratory analysis), especially
when derived from a groundwater source. Additionally, plant tissue and soil
nutrient analyses may serve as an indispensable tool to address and, if needed,
compensate for the nutrient loss caused by irrigation. Finally, there is an
urgent demand for research regarding groundwater quality and its relationship
with crop production, in order to develop a more thorough understanding of the
impacts and consequences of the drought and our current agricultural practices.
Such research could be crucial in ensuring the future of California
agriculture, and ultimately, the future of the entire country.
Literature
- Bawden, G.W., Sneed, M., Stork, S.V., Galloway,
D.L., Measuring human-induced land subsidence from space, 2003.
- Carle, D., 2004. Introduction to water in
California. Univ. of California Press, Berkeley, 262 p.
- Davis, U.C., Drought impact study: California
agriculture faces greatest water loss ever seen, in
http://news.ucdavis.edu/search/news_detail.lasso?id=109782015.
- Leake, S.A., Konieczki, A.D., Rees, J.A.,
Desert basins of the Southwest, 2000, US Geological Survey.
- Porvair, F.G., 2015. Porvair filter helps
stricken California farmers tackle drought. Membrane Technology 2015, 6.
- USDA, Food price Outlook, in
http://www.ers.usda.gov/data-products/food-price-outlook/summary-findings.aspx2015.
AGQ Labs USA
Agronomy Department
805-816-4578
