Vulnerability of coastal aquifers to groundwater use and climate change

[sskasser]

http://www.nature.com/nclimate/journ...imate1413.html

Vulnerability of coastal aquifers to groundwater use and climate change


Grant Ferguson & Tom Gleeson

Journal name:Nature Climate Change
Year published: 2012
DOI:doi:10.1038/nclimate1413
Received 21 April 2011
Accepted 18 January 2012
Published online 19 February 2012

Climate change and human population growth are expected to have substantial impacts on global water resources throughout the twenty-first century1, 2. Coastal aquifers are a nexus3 of the world’s oceanic and hydrologic ecosystems and provide a water source for the more than one billion people living in coastal regions4, 5. Saltwater intrusion caused by excessive groundwater extraction is already impacting diverse regions of the globe5, 6, 7. Synthesis studies8, 9 and detailed simulations10, 11, 12, 13 have predicted that rising sea levels could negatively impact coastal aquifers through saltwater intrusion and/or inundation of coastal regions. However, the relative vulnerability of coastal aquifers to groundwater extraction and sea-level rise has not been systematically examined. Here we show that coastal aquifers are more vulnerable to groundwater extraction than to predicted sea-level rise under a wide range of hydrogeologic conditions and population densities. Only aquifers with very low hydraulic gradients are more vulnerable to sea-level rise and these regions will be impacted by saltwater inundation before saltwater intrusion. Human water use is a key driver in the hydrology of coastal aquifers, and efforts to adapt to sea-level rise at the expense of better water management are misguided.

Figures at a glance

1. Figure 1: Coastal aquifers are affected both by groundwater extraction and sea-level rise. a,b, Conceptual model used for simulating the impact of groundwater extraction (a) and sea-level rise (b) including both saltwater intrusion and saltwater inundation. The simulation variables include discharge per unit coastline (q), groundwater extraction rate (Q), aquifer thickness (b), the difference in hydraulic head between the inland boundary of the flow system and the coast before sea-level rise (Δho), and the distance from the coastline to the well (xi)and the toe of the saltwater wedge (xt). The grey area shows the distribution of the fresh aquifer water before extraction or sea-level rise.
   
2. Figure 2: Present saltwater intrusion areas have a high population density and/or low hydraulic gradients. a, For coastal watersheds in the contiguous United States, hydraulic gradients >0.001 are mapped in blue and those with hydraulic gradients <0.001 are mapped in red. Insets showing watershed boundaries in the Pacific northwest and the Florida panhandle are provided as more detailed examples. b,c, The distribution of hydraulic gradients and population densities along the west coast (b) and east coast (c) of the contiguous United States. Documented saltwater intrusion locations7 are labelled with black squares in a and grey bars in b and c.
   
3. Figure 3: The impact of groundwater extraction on coastal aquifers is more significant than the impact of sea-level rise. a, Saltwater intrusion for various hydraulic gradients with extraction from a well 1 km from the coast in a 10-km-long watershed (Supplementary Table S1). Grey area denotes changes in recharge of ±30%. Inset histogram summarizes coastal hydraulic gradients (Fig. 2a)20. b, Saltwater inundation and associated infiltration of sea water will be more important than saltwater intrusion from sea-level rise assuming equal topographic gradient and hydraulic gradients. c, Hydraulic gradients for watersheds adjacent to the US Gulf Coast with red indicating greater vulnerability.
   
4. Figure 4: The uncertainty owing to different aquifer types is significant as shown by simulation of these types over a range of coastal populations.

[scottj]

Saw this in action over the last few paddles on the Waccasassa and Ochlockonee rivers. Trees along the gulf coast are dying as the salt water rises and the fresh water sheet flow reduces. Also the water coming out of the wells along the Ochlocknee river got more "rotten egg" smelling as we got toward the coast, probably a sign that lots of bacteria in the caves under us were feeding off that salt/fresh boundary and pissing hydrogen sulfide out.

[scottj]

Let me add to this if you love cave diving:
1. Don't water and/or fertilize your lawn. Plus who wants to spend a Saturday mowing the lawn when you could be diving
2. Get an efficient vehicle. You would be amazed by how many tanks you can fit in the back of a Prius! Plus all that cash not spent on gas can be spent on gas (for diving)

[tflaris]

Let me add to this if you love cave diving:
1. Don't water and/or fertilize your lawn. Plus who wants to spend a Saturday mowing the lawn when you could be diving
2. Get an efficient vehicle. You would be amazed by how many tanks you can fit in the back of a Prius! Plus all that cash not spent on gas can be spent on gas (for diving)

Especially #1.


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I am here: http://tapatalk.com/map.php?q0mxlb

[sskasser]

California is already experiencing contamination:

Report: Calif. nitrate contamination spreading

By Gosia Wozniacka
Associated Press / March 13, 2012


FRESNO, Calif.—Nitrate contamination of drinking water is a pervasive problem in California's agricultural heartland and is bound to intensify in the coming years, according to a University of California, Davis study released Tuesday.




The study, ordered by the state Legislature, shows chemical fertilizers and livestock manure are the main source of nitrate contamination in groundwater for more than 1 million Californians in the Salinas Valley and parts of the Central Valley.


While nitrate problems have been known for decades, the study offers a comprehensive assessment of how many people are exposed and identifies solutions and costs.


"In the near future, this problem is going to persist and is likely to get worse," said Thomas Harter, UC Davis groundwater hydrologist and the study's lead author. "Even if we were to eliminate all the sources of nitrate that we have today, we would still be dealing with this issue."


Nitrates are found naturally in some foods, but scientists have linked high levels of nitrates to "blue baby syndrome," reproductive disorders and cancer. Infants who drink water that exceeds the nitrate standard could become seriously ill and die, according the U.S. Environmental Protection Agency. State health officials say they don't track illnesses associated with nitrates.


The study -- covering the Salinas Valley and Fresno, Tulare, Kings and Kern counties -- concluded half of the 2.6 million people in those areas live in communities where raw drinking water sources have registered nitrate levels exceeding the standard. Many of those communities blend or treat their water, drill a new well or provide another alternative source, passing on the extra costs to rate payers.


Some wells in Fresno, population 500,000, have exceeded the nitrate standard. The city put a number of out of service, expanded its use of surface water and blended water from active contaminated wells with that in other wells.


The study also found about one in 10 people in the study area rely on untreated groundwater that may exceed the nitrate standards. Most are residents of small, poor agricultural communities which cannot afford to treat the water or offer alternatives.


"I grew up with contamination in my water and to think that I have to put in extra money just to make sure my child is going to be OK, it really bothers me," said Jessica
Sanchez, a pregnant resident of East Orosi, an unincorporated farmworker community of 500 in Tulare County, where the two existing wells regularly exceed the safe standard for nitrates.


Sanchez, a college student, said her family pays $60 a month for contaminated water while spending at least that amount on bottled water for cooking and drinking.


If nothing is done, the study concludes, the financial burden on many agricultural communities could increase. By 2050, nearly 80 percent of the population -- about 2 million residents -- in the study area could have nitrate contamination exceeding the state standard.



"It shows how huge the scope of the problem is," said Laurel Firestone, co-director of the Community Water Center, a nonprofit advocating for safe drinking water in the Central Valley. "We need our drinking water sources, we rely on them daily. This contamination has been out of sight, out of mind for too long."


Cleaning up polluted aquifers would be too difficult, the study concludes. Improved farming practices and water blending, treatment and alternative water sources are more cost effective.


But treatment, Harter said, is very expensive, as is drilling a new or deeper well. Most at-risk communities like East Orosi don't have the means to make changes.


The state and regional water boards should assist those communities, Harter said, by providing legal and technical support and funding for solutions such as hooking up to larger communities for alternative water sources.


The study estimates addressing current nitrate contamination will cost the state $20 million to $35 million per year. The study proposes a fertilizer tax which would be used by affected communities to mitigate for nitrate contamination. Another funding option is water use fees from affected residents.


The study found that nitrate leaching from agricultural land is responsible for 96% of current groundwater contamination. And while fertilizer use has leveled off in recent years, the amount of dairy manure has increased, making for a net increase over the past decade in nitrates loaded into the ground.


That means contamination of drinking water will increase in future years, Harter says, because it takes time for nitrates to migrate.


California farmers say they have worked to change their farming practices to address the problem.


"There's a lot of energy all over the country on this issue and there's a host of people developing new technologies," said Hank Giclas, senior vice president of Western Growers.


Bob Martin, general manager of Rio Farms in King City, said he tests to find out how much nitrate the soil has and how much fertilizer, if any, it needs. This allows him to target the timing of the fertilizer and to reduce the amount used, Martin said.


His farm also spent about $11,000 last year on soil moisture probes used during drip irrigation. The sensors showed the farm was over-irrigating certain crops, meaning more nitrates were moving beyond the root zone and into the groundwater.


"We want to be good stewards of the land and we're doing everything we can," Martin said.


© Copyright 2012 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

[Jay]

Ehhh, I am in the Biscayne Aquifer. My well water (for irrigation) already smells like crap.