The stunted growth of coral reefs.

 
New York City shelters its 8.3 million residents within a complex, three-dimensional matrix of concrete and steel. Construction crews must work on the integrity of the city’s structural skeleton constantly just to keep up with growth and age. Like a living organism, the city is expanding up, down and outwards while repairing and replacing decrepit trusses and frames with new, high quality materials.

It is a common big-screen fantasy to imagine the physical decay of New York City if these construction efforts were to suddenly cease in some kind of post-apocalyptic madness. However, the structural collapse that would bring New York City back to nature is actually occurring within nature, and you don’t need CGI graphics to imagine it. Just last week a team of scientists shared new findings that warming oceans are reducing the size and strength of coral reefs in two different parts of the world.

A coral reef is not unlike a city. Reefs are massive underwater edifices that support a stunning diversity and density of organisms. But instead of using building materials like concrete and steel, coral reefs house their residents within and upon a skeleton of calcium carbonate. This calcium carbonate is continually laid down by the reef's construction crew – growing colonies of coral polyps.

Individual coral polyps are actually small, soft-bodied animals that grow affixed to a hard surface. For protection they secrete calcium carbonate near their base. This calcium carbonate accumulates as the polyps grow, clone themselves, and multiply into large colonies. Over many generations, the calcium carbonate left behind becomes the skeleton of the reef, which still consists of a living colony of coral polyps on the surface.

The ability of coral polyps to produce calcium carbonate, called calcification, depends on a host of environmental factors. For example, seasonal differences in water temperature cause calcification to increase in the summer and decrease in the winter, resulting in alternating layers of high and low calcium carbonate density. It creates a pattern similar to the annual growth rings of a tree. The scientists used this pattern to measure the extent of growth and the density of calcium carbonate produced every year by coral colonies. They focused on two genera, Porites and Montastraea, from the Great Barrier Reef and Mesoamerican Barrier Reef. They compared these annual growth data to existing records of warming sea surface temperatures spanning at least a decade.

One of the coral genera, Porites, showed the greatest sensitivity to warming temperatures regardless of location. In both the Great Barrier Reef and the Mesoamerican Barrier Reef, Porites experienced sharp declines in calcification rate as sea surface temperatures increased. If climate change models are correct, at the given rate of decline, Porites in the Great Barrier Reef will stop laying down calcium carbonate entirely by 2100. In the warmer Mesoamerican Barrier Reef, calcification by Porites will cease in 2060. The genus Montastraea has also experienced reduced rates of calcification, although not as extreme. Montastraea in the Mesoamerican Barrier Reef will experience a 40% reduction in calcification by 2100.

The consequences of reduced calcification will manifest differently in the two genera. As temperatures rise, Porites produces calcium carbonate at the same density, but compensates for reduced calcification by not extending as far. Therefore, Porites reefs will grow more slowly and could be outcompeted for space by other organisms. Montastraea continues to extend in warmer temperatures, but it does so at the expense of calcium carbonate density. Much like osteoporotic bones, a Montastraea reef with reduced calcium carbonate density is more susceptible to physical and biological damage. Warming water temperatures will compromise both types of reefs in their ability to support biodiversity, either in terms of space or strength.

As grim as they seem, these predictions are likely conservative. The scientists mention that they don’t consider other factors that affect calcification such as coral mortality, coral bleaching, disease, and the negative consequences of pollution, erosion and other environmental concerns. The slow decline of coral reefs may not be fodder for a disaster flick, but piles of stunted, brittle coral reef will be utterly disastrous for the world’s oceans in a time that is already considered a biodiversity crisis.

Carricart-Ganivet JP, Cabanillas-Tera´n N, Cruz-Ortega I, Blanchon P (2012) Sensitivity of Calcification to Thermal Stress Varies among Genera of Massive Reef-Building Corals. PLoS ONE 7(3): e32859. doi:10.1371/journal.pone.0032859 

Photo: A view of the Mesoamerican Barrier Reef, Belize en.mesoamericanreef.org

Pharmaceuticals without a prescription.

As the population ages, healthcare spending swells, and medical technology advances, the use and variety of pharmaceuticals and personal care products (PPCPs) grow to meet the demand of people worldwide. Like all products, the presence of PPCPs in the environment has become as ubiquitous as their use in the human population. Today it is likely that PPCPs are detectable at low levels in all waterbodies adjacent to human settlement. In some instances they have been found to reach concentrations that rival pesticides.

PPCPs enter the environment primarily through the wastewater stream. When a pharmaceutical is administered to a patient, as much as 90% of the dose can be excreted still in its active form. Even the portion that is metabolized can be transformed and excreted as a unique byproduct. Personal care products like shampoos and lotions enter the wastewater stream when we wash our bodies and hands. This ever-changing concoction of chemicals, from analgesics to antibiotics, lipid regulators to synthetic musks, continuously buffets wastewater treatment plants, most of which are only designed to remove conventional pollutants and the basics of human waste. Due to the variety and the novelty of compounds found in PPCPs, many of these chemicals pass through traditional wastewater treatment plants unchanged and enter our streams, rivers, bays, and oceans. A 2009 study by the San Francisco Estuary Institute found 18 common PPCP compounds in treated wastewater effluent and surface water in the South San Francisco Bay. These included acetaminophen (Tylenol), fluoxetine (Prozac), and gemfibrozil (Lopid).

Even though PPCPs are generally detected at low concentrations in our waterways, we cannot be sure of their impact on the environment because their effect on non-human organisms is unknown. People are warned for good reason not to take pharmaceuticals without a prescription or in combination with other drugs, because the synergistic effects can be lethal. But what happens to a Chinook salmon that takes a low dose of Lipitor? And what if that Lipitor is mixed with dozens of other unidentified pharmaceuticals in the water? Because of the seemingly low risk to humans and the sheer number of compounds to be studied, research on the environmental fate of PPCPs is limited and regulation is nonexistent.

A recent study by a team of researchers from Eötvös Loránd University in Budapest and the China University of Geosciences suggests that the risk of residual PPCP exposure to humans may be greater than we think. In some parts of the world, where groundwater supplies must stretched to meet the demand for potable water, riverbank infiltration is seen as a safe and practical method to speed up the recharge of an aquifer. Instead of harvesting drinking water directly from the river, where a wastewater outfall may discharge treated effluent just upstream, water is pumped from wells adjacent to the riverbank, which lowers the water table, changes the pressure gradient, and pulls water from the river into the aquifer. Riverbank infiltration uses the soils of the bank to filter out pathogens, heavy metals, excess nutrients, hydrocarbons, and other pollutants in the same way that stormwater is purified as it naturally percolates through soil; however, with riverbank infiltration this process happens quickly enough to meet the population's needs. Budapest supplies one third of its groundwater through riverbank infiltration of the Danube River, which also receives effluent from two wastewater treatment plants.

Over the course of a full year, Margit Varga and her team sampled water from the Danube River and sediments from within two meters of the bank at three sites adjacent to riverbank infiltration wells. Many PPCP compounds are removed from water when they stick to sediments; however, the research group tested their samples for the presence of four acidic drugs, which have a greater affinity for water and are less likely to grab onto the particles of soil. Three of these drugs - ibuprofen, naproxen, and diclofenac - were regularly detected in the river water. The highest concentrations occurred during the winter when the water level was relatively low and cold temperatures restricted microbial activity that could degrade the compounds. Naproxen and diclofenac were also detected in the sediment samples, suggesting that some amount of these acidic drugs are removed from the water during riverbank infiltration.

The concentration of these drugs in the sediment seemed to be influenced not only by their initial concentration in the water being pulled through the bank, but also by the concentration of total organic carbon in the sediment. Sediment with a high concentration of carbon was more effective at filtering out the drug compounds. Sandy sediment with low carbon content could allow PPCPs to penetrate further into the bank. It is well-known that sediments have different compositions and different abilities to filter out contaminants - this concept has been applied countless times to septic systems and stormwater treatment mechanisms. But Varga's study confirms that the same is true for PPCPs, which are unregulated, poorly understood, and still in the vague category of "contaminants of emerging concern." Given the right combination of low water levels, cold temperatures, increased use of PPCPs, and poor sediment filtration capacity, these compounds could very likely reach drinking water supplies in areas that depend on riverbank infiltration. And as growing demand for potable water brings human populations closer and closer to their treated (or untreated) wastewater, the only way to eliminate the risk of exposure might be the remove PPCPs from the waste stream entirely before they can reach the environment.

Varga, M., Dobor, J., Helenkar, A., Jurecska, L., Yao, Jun., & Zaray, G. (2010). Investigation of acidic pharmaceuticals in river water and sediment by microwave-assisted extraction and gas chromatography-mass spectrometry Microchemical Journal DOI: 10.1016/j.microc.2010.02.010

Photo courtesy of Carly & Art via Flickr