Crawford J.T.,University of Wisconsin - Madison |
Crawford J.T.,U.S. Geological Survey |
Lottig N.R.,Center for Limnology |
Stanley E.H.,University of Wisconsin - Madison |
And 4 more authors.
Global Biogeochemical Cycles | Year: 2014
Aquatic ecosystems are important components of landscape carbon budgets. In lake-rich landscapes, both lakes and streams may be important sources of carbon gases (CO2 and CH4) to the atmosphere, but the processes that control gas concentrations and emissions in these interconnected landscapes have not been adequately addressed. We use multiple data sets that vary in their spatial and temporal extent during 2001-2012 to investigate the carbon gas source strength of streams in a lake-rich landscape and to determine the contribution of lakes, metabolism, and groundwater to stream CO2 and CH4. We show that streams emit roughly the same mass of CO 2 (23.4 Gg C yr-1; 0.49 mol CO2 m-2 d-1) as lakes at a regional scale (27 Gg C yr-1) and that stream CH4 emissions (189 Mg C yr-1; 8.46 mmol CH 4 m-2 d-1) are an important component of the regional greenhouse gas balance. Gas transfer velocity variability (range = 0.34 to 13.5 m d-1) contributed to the variability of gas flux in this landscape. Groundwater inputs and in-stream metabolism control stream gas supersaturation at the landscape scale, while carbon cycling in lakes and deep groundwaters does not control downstream gas emissions. Our results indicate the need to consider connectivity of all aquatic ecosystems (lakes, streams, wetlands, and groundwater) in lake-rich landscapes and their connections with the terrestrial environment in order to understand the full nature of the carbon cycle. ©2014. American Geophysical Union. All Rights Reserved.
Torn K.,University of Tartu |
Kovtun-Kante A.,University of Tartu |
Herkul K.,University of Tartu |
Martin G.,University of Tartu |
Maemets H.,Center for Limnology
Aquatic Botany | Year: 2015
Material collected during the years 1995-2011 was used to describe the distribution and environmental preferences of charophyte species in Estonian lakes and its coastal Baltic Sea. Altogether 22 species of charophytes were found in Estonian waters. Five taxa occurred in less than 10 localities and were classified as rare. Chara aspera and Tolypella nidifica were the most frequent and widespread species. The majority of species preferred shallow water less than 1m in Estonian lakes and the coastal sea. Mud was the prevailing substrate on locations where charophytes were found, sandy substrate was characteristic for species which tolerate more exposed localities. Most of freshwater species preferred water alkalinity over 80mgHCO3 -l-1. A model was developed to predict the probability of the occurrence of Chara spp. in the extent of the whole Estonian marine waters based on several environmental variables. Boosted regression trees (BRT) was chosen as the modelling technique. Based on the model prediction, the vast majority of charophyte habitats are situated in the sea areas of the West Estonian Archipelago. That sea area is characterized by favourable conditions for charophytes: high proportion of shallow areas protected from wave exposure. © 2014 Elsevier B.V.
It’s just a flea, no bigger than a speck. But it eats like a hog. That’s a problem because what the invasive spiny water flea from Europe and Asia likes to eat most is one of the coolest and most beneficial life forms in the food chain of Wisconsin’s Lake Mendota, the Daphnia flea. The victim grazes on algae, and the more it eats, the better the lake’s water quality and visibility, making recreational pastimes such as swimming and fishing more pleasurable. Since their arrival in cargo ships that sucked up fresh water in Europe and the Far East and dumped it in the Great Lakes, spiny fleas have reduced the biomass of Daphina so much that algae growth has spiked, and Lake Mendota’s visibility has clouded, further impairing a resource on which humans and animals rely. Once people could see their toes in water that was chest high as opposed to about thigh high, said the author of a new study that shows how invasive species like the spiny water flea does a lot more damage than people know. The author, Jake Walsh, a researcher at the Center for Limnology at the University of Wisconsin, said it’s hard to explain just how destructive the flea has been over the past 30 years unless you describe it in a way the average person would understand. [The Dirty Dozen: 12 of the most invasive animals in the United States] His team used models to estimate the cost of limiting the algae that Daphnia would eat. Algae relies on phosphorous to grow, and much of that runs off cities and farms in sewer waste water and animal excrement, to name just a few things. Reversing algae overgrowth in Lake Mendota would require a 71 percent reduction in its phosphorous pollution. “A phosphorous reduction of this magnitude is estimated to cost between $86.5 million and $163 million,” the study says. Those estimates “may increase considerably if cases of secondary invasions into inland lakes, such as Lake Mendota, are included. That’s not even the half of it. At least 180 species of invasive animals have been introduced into the Great Lakes by ships that travel across the world. At the root of the problem are humans, who, some argue, are the most destructive invasive species of all in the Americas. Like numerous other researchers, Walsh’s team blamed phosphorus pollution degrading the quality of lakes and reservoirs, cheapening their aesthetic value, not to mention property values. Algae blooms lead to fish kills that stymie sportsmen and beach closures that hurt swimmers. Blooms can release toxins harmful to humans and fish, and they can suck so much oxygen from water that fish and other animals can’t survive. Dumping an animal that preys on algae grazers made a bad situation much worse, they said. Using the spiny flea as an example, the authors emphasized that all invasive species wreak havoc in a way that few have considered. Walsh mentioned the emerald ash borer off the top of his head. Its march across the Midwest since 2002 has left billions of nickel-sized holes in the ash trees they bore into, killing trees that provide durable wood for home flooring, bowling alleys, church pews, baseball bats and electric guitars. Moreover, they ruin trees adorning sidewalks and front yards, hurting the appeal of cities, not to mention the carbon the trees capture to help improve air quality. The list goes on. Pythons are marauding across the Everglades. Nutria — a swamp rat — are proliferating in Louisiana and the on Delmarva Peninsula. The Northern snakehead fish is threatening the Chesapeake Bay and rivers in the Mid-Atlantic. Feral hogs are on the march in Texas, Florida and Georgia and are moving into Virginia. And the Asian citrus psyllid has caused “a yellow dragon disease” called huanglongbing that’s killing orange trees in Florida, the source of 80 percent of the nation’s orange juice. That is by no means the entire list; it’s only a few. [How greedy and destructive wild pigs became ‘the most invasive animal in the U.S.’] The spiny flea, which drags a skinny tail, is about as big as the width of a pinky finger, Walsh said. The paper called it a voracious eater that can consume more microscopic organisms called zooplankton than fish and any other life forms that prey on them combined. Its gluttony alters an entire lake food web, making eutrophication, an explosion of aquatic plant growth made worse by chemicals used by humans. “Freshwater ecosystems are a cornerstone of human society,” the new study says, used for “drinking water, fisheries, pollution dilution, recreation,” among other things. Policymakers haven’t estimated their true value, “leaving them overlooked and poorly integrated” into the decisions they make on behalf of residents. Decisions, Walsh said, like attempting to eradicate harmful invasive species. The economy is growing but carbon emissions aren’t. That’s a really big deal This Galapagos island — named Darwin — will now anchor a vast new marine reserve This huge change in how we get energy is coming much faster than expected For more, you can sign up for our weekly newsletter here, and follow us on Twitter here.
Catherine Wagner, a UW assistant professor in the Department of Botany and the UW Biodiversity Institute, is studying interactions between the biodiversity of East Africa's Lake Tanganyika and the human communities that live around the lake. The work is conducted with the support of The Nature Conservancy and with collaborator Peter McIntyre, an assistant professor in the University of Wisconsin-Madison's Center for Limnology. Lake Tanganyika is 418 miles long, almost a mile deep and holds 18 percent of the world's unfrozen surface freshwater. "Many animals in the lake evolved there and are found nowhere else in the world," Wagner says. "They are endemic to the lake." This holds true for the majority of the lake's more than 300 fish species. Wagner and colleagues are studying two species of endemic sardines, which are the most abundant fish in the lake's open water zone. "My role in the project is to use genetics to understand spatial patterns within these fish populations," Wagner says. "We take samples from natural populations to see to what extent the lake is composed of single large populations versus very local populations. Although these fish are the main source of protein for the millions of people living around the lake, we know very little about their movement within this very large fishing area. Understanding this basic biology is an important step toward ensuring that they can be sustainably managed." Wagner says one species of sardine spawns in the lake's open water, while another spawns near the shore. Juveniles of both species live near the shore. Once mature, the fish move to the open water. Sardines are the predominant source of protein for communities that live near the lake. Fishing at night, fishermen use large lift nets, and frequently pull up fish by the thousands in a single draw of the net. "They (fishermen) take everything, including the Nile perch, which are the predators of the sardines," Wagner says. "The issue is that these catches have been declining. There is debate over whether the fish are declining due to overfishing, because the lake is warming, or both. "Decreased catch rates have led to communities increasingly fishing near shore. In some places, they're catching the sardines as juveniles rather than adults," she says. "We are interested in what impact this has on the populations, and that we need to study the patterns of movement in juveniles and adults in the lake." With this information, it may be possible to designate protected areas that are important for juvenile growth. To understand that dynamic, Wagner says researchers have to understand where the juvenile sardines are growing up or maturing, and the degree to which there is local adaptation within these populations. "If we catch the fish in the north (part of the lake), are they coming from the shore as juveniles in the north, or have they grown up in many different areas of the near-shore zone?" Wagner asks. "We have no idea how much the fish move during their lifetimes, or if they return to spawn where they were born." Within Mahale Mountains National Park boundaries (the park is located in Tanzania), there is a strictly enforced 'no fishing' policy. Those near-shore areas within the park are being used as baselines to measure fish numbers, to compare with locations outside the park where fishing is allowed, Wagner says. "One thing that is clear: Just from observing fish while snorkeling, there appears to be a much higher abundance of fish in no-fishing zones," Wagner says. The Nature Conservancy, which funds the project called TUUNGANE, is working to understand the impacts of fishing on fish populations in the lake, and working with communities to develop plans that are beneficial for people and for sustainable biodiversity, Wagner says. Lake Tanganyika not only is the second largest freshwater lake in the world, but it also is the second oldest, dating 9 million to 12 million years old, Wagner says. Only Lake Baikal, in southeastern Siberia just north of the Mongolian border, is older and larger among freshwater lakes. Both are considered rift lakes, meaning they are located in parts of the Earth that are splitting apart, Wagner says. Lake Tanganyika is bordered by four countries. Most of the eastern portion of the lake is located in Tanzania; the north bordered by Burundi; the western shore is the Democratic Republic of Congo; and the southern part of the lake crosses into Zambia. In addition to fish, the lake is home to crocodiles, water cobras and hippos.During their sampling this past summer, Wagner and other researchers were primarily based in Kalya, a village located south of the national park.Julian Junker, a visiting researcher from EAWAG, the Swiss National Institute for Aquatic Science and Technology in Lucerne, Switzerland, says the political history of these countries has, in some places, directly influenced the amount of fishing occurring. In Burundi, unrest during the last decades drove thousands of people away from the shores of Lake Tanganyika. When the situation stabilized, returning farmers, in some cases, shifted from farming to fishing. "In 2003, there were 40,000 fishermen in the area," says Junker, who is assisting Wagner with this lab research. "In 2011, there were 95,000 fishermen." Explore further: What happened to Lake Champlain's native trout?
The findings suggest a need to recalculate the cost of invasive species. "Our study indicates that previous attempts to put a price tag on invasive species impacts haven't come close to the true cost," says Jake Walsh, a Ph.D. candidate at the UW Center for Limnology and lead author of the report, published in the Proceedings of the National Academy of Sciences. The study might also inform the conversation about costs and benefits of the Great Lakes shipping industry. For decades, oceangoing ships have brought tons of cargo and tens of millions of dollars into the Great Lakes economy each year. But that manmade connection between the Great Lakes and the Atlantic Ocean has also helped bring in more than 180 non-native species. Most studies, Walsh says, have focused only on invasive species that live in the five Great Lakes and looked just at direct costs of managing them—like the $20 million spent each year to poison invasive sea lamprey. Instead, Walsh and his colleagues turned their attention to secondary invasions, or places where invasive species have moved since their introduction to the Great Lakes. The researchers also added "ecosystem services," the benefits that humans derive from natural resources, to the equation. For example, Lake Mendota in Madison is essential to both the local economy and residents' quality of life—supporting pursuits like fishing, boating, swimming and recreation along its shores. Clear, clean water is the key ingredient to all of these ecosystem services. However, since at least 2009, Lake Mendota has been invaded by a tiny, voracious zooplankton called the spiny water flea. Originally from Russian lakes, the invader made its way to the Great Lakes in the ballast water of oceangoing cargo ships, historically a major vector of Great Lakes invasive species introductions. The spiny water flea then moved inland in boats or bait buckets and now feasts on a native species of zooplankton called Daphnia pulicaria. Left to their own devices, says Walsh, daphnia help "clean" the lake by eating huge amounts of algae—so much, in fact, that they create clear water. Today, however, Lake Mendota's daphnia are falling prey to the spiny water flea before they can take their toll on algae. Complicating matters is agricultural fertilizer that runs into the lake. This fertilizer contains lots of phosphorus, which promotes the growth of algae just as well as corn or soybeans. These high-fertilizer, low-daphnia conditions add up to a dramatic decline in water clarity and a sharp rise in algal blooms. Currently, there is no way to rid a lake of billions of nearly microscopic zooplankton short of poisoning the entire body of water. But there are land use practices and technologies available to reduce phosphorus runoff. Through statistical modeling, the researchers determined that it would take a 71 percent reduction of phosphorus to return Lake Mendota's water quality to pre-invasion conditions. Stemming that flow comes at a steep price—anywhere from $80 million to $163 million dollars. It's a big number, Walsh concedes, but "it gives us a clearer understanding of the 'true cost' of invasive species." While only a fraction of the 180 species that have entered the Great Lakes have become nuisance enough to be labeled "invasive," their collective impact is staggering, says Walsh. "There are hundreds of billions of dollars' worth of damages we can account for right now. If you add in invasive species' impact on ecosystem services and look at secondary invasions, then that number is likely to be trillions," he says. In spite of the staggering sticker shock, Walsh sees a silver lining. Many invasive species eradication or control efforts have been deemed too expensive to entertain researching or implementing them. But, Walsh says, if the price of not fighting these invasions is as high as his study indicates, "maybe we have a much bigger budget than we thought we did." Explore further: Invasive species spreads to Vilas County lake in Wisconsin More information: Invasive species triggers a massive loss of ecosystem services through a trophic cascade, www.pnas.org/cgi/doi/10.1073/pnas.1600366113