Anoxic Conditions in the Northern Gulf of Mexico Predicted to Increase as Climate Change Continues

Climate change projected to exacerbate impacts of coastal eutrophication in the northern Gulf of Mexico

Arnaud Laurent, Katja Fennel, Dong S. Ko, John Lehrter

Summarized by Kristina Welsh, who is currently a junior at Binghamton University pursuing a B.S. in Environmental Science with a concentration in Natural Resources and a minor in GIS. Kristina hopes to pursue a job involving field work and travel opportunities. In her free time, Kristina enjoys camping, biking, and hanging out with her dog, Bailey.

What data were used: This study uses data from past published articles to compare present and future conditions intheGulf of Mexico. A present condition model was created using data from the Intra-Americas SeaNowcast-Forecast System. The future model was constructed using data from MPI-ESMRPC 8.5.

Methods: This study uses two 6-year physical-biogeochemical model simulations from the Regional Ocean Modeling System to represent present and future conditions in the northern Gulf of Mexico. Initial and open boundary conditions, river discharge, atmospheric temperature and pCO2 (atmospheric carbon dioxide) were variable in both models; all other factors were kept constant. The present simulation, which covers the period of 2005-2010, uses data from the Intra-Americas Sea Nowcast-Forecast System. The future simulation represents a 6-year period at the end of the century. The future model parameters were set with a 10% increased discharge from the Mississippi River, an air temperature increase of 3 ºC, and an atmospheric pCO2 increase to 935.85 µatm. Although conditions of river nutrient load were kept the same, the increased river discharge in the future model will dilute nutrient concentration results.

Four models (present on left, future on right) that show modeling results.
This figure illustrates the pH decrease in bottom waters that is predicted to occur in the future simulation. The bottom row shows how oxygen concentrations are expected to decrease.

Results: The future models predict a summer surface and bottom water temperature increase by 2.69ºCand 2.23ºC, respectively. The salinity of surface waters decreases by 0.48 due to an increase in freshwater river discharge in the model. As salinity in bottom waters is controlled by the saltier offshore water, only a decrease of 0.02 was observed. The reduced density of the warmer and fresher water lead to an increased stratification in summers by +12.35 J m^-3. These warmer waters cause lower oxygen saturation levels and thus lower oxygen concentrations, with summer surface oxygen concentrations 3.4% lower than the present average. The decrease in surface water oxygen saturation leads to a 9.4% decrease in oxygen concentrations in bottom waters. 60-74% of the decrease in oxygen concentration is a result of saturation-dependent effects, while the other 26-40% is a result of changes in biological rates and stratification. Lower oxygen concentrations in the Gulf of Mexico leads to an increase in extent and duration of future hypoxia conditions. Hypoxic areas increase by 26% and volume increases by 39%, resulting in more frequent anoxic surface and bottom waters. The future model increased surface pCO2 and alkalinity, causing a decrease in bottom water pH range of 0.37-7.58, with large spatial and temporal variability. Hypoxic waters in the Gulf predict an average pH 7.39. Present and future conditions vary year to year due to different along shore wind directions, upwelling, and river discharge, but overall follow the same trend.

Why is this study important? This study implies how human-induced climate change will exacerbate hypoxic conditions and eutrophication-driven acidification in the northern Gulf of Mexico by the end of the century. Future hypoxic conditions will create growth and reproductive impairment to many sensitive species living in the Gulf. Changes in atmospheric CO2 can influence ocean pH and air temperatures, producing other negative effects on water chemistry, and plant, and animal life, creating a positive feedback system that will exacerbate these changes. 

The big picture: This study adds to our understanding of the risks of climate change. As this model interprets the impacts of climate change on nature and human sustainability, we can visibly see how the Earth’s oceans will change globally as well as locally. This article gives us evidence as to why we need to take action now so these changes do not occur.

Citation: Laurent, A., Fennel, K., Ko, D. S., & Lehrter, J. (2018). Climate change projected to exacerbate impacts of coastal eutrophication in the northern Gulf of Mexico. Journal of Geophysical Research: Oceans, 123(5), 3408–3426. https://doi.org/10.1002/2017jc013583

Colonization and Sea Level Rise Effects on Carbon Storage in Freshwater Wetlands of Southeastern United States

The Impact of Late Holocene Land Use Change, Climate Variability, and Sea
Level Rise on Carbon Storage in Tidal Freshwater Wetlands on the Southeastern United States Coastal Plain

Miriam C. Jones, Christopher E. Bernhardt, Ken W. Krauss, Gregory B. Noe

Summarized by James Myers who is a graduate student at Binghamton University earning his masters in teaching for earth science. As an undergraduate he majored in environmental
chemistry. Not long after he decided he wanted to become an educator and work towards
creating the next generation of environmental scientists. In his downtime he enjoys playing
guitar, camping, and watching hockey.

What data were used: Sediment cores were collected along the Waccamaw River in South Carolina and the Savannah River in Georgia. The sites were chosen because they have similar landscapes, ranging from freshwater, to moderate salinity, and oligohaline marsh. Four piston core samples were taken from the Waccamaw River, one that was found in freshwater, one in moderately salt-impacted water, and two from the Sampit River, one from a heavily salt-impacted area and one from an oligohaline marsh. Four other cores were collected along the Savannah River using a peat corer. These core sites were also from freshwater, moderately salinated, highly salinated, and an oligohaline marsh.

Three maps of the Savannah river, Waccamaw River, and an inset map showing the location of both rivers along the southeastern United States.
Maps designating the locations of the sites sampled. The sites are roughly 150 km away from each other, along the southeastern coastline of the United States. The Savannah River sites are found further upstream compared to the Waccamaw River sites. The cores at both locations were assigned numbers from one to four. The lower numbers are further upstream and are lower in salinity.

Methods: The cores were dated using radiocarbon analysis on macrofossils and bulk sediment which helped determine which samples were from the colonial era. Time scales were reported with calibrated years before present from 1950. Core compression was apparent within the samples, and bulk density (weight of sediment in a given volume) and accretion rates (how fast sediment accumulates) were adjusted to account for this. Carbon content was calculated using the loss on ignition method. Carbon accumulation rates were calculated by multiplying the percent carbon by the bulk density and accretion rate determined from an age-depth model. Pollen analyses were run to understand which plant species lived at these sites over time, as this method revealed what the environment must have been like if certain plants and trees were able to survive.

Results: The core samples from the Waccamaw river dated between the last 1,100-4,200 years. The oldest sample was the heavily salt-impacted site, which began as a back swamp environment, where fine silts and clays settle after flooding which create a marsh-like landscape. This was determined from the presence of Nyssa, Taxodium, and Poaceae pollen. The accumulation rates are low, but still higher than the freshwater sites. Upper freshwater and oligohaline sites were also found to have been back swamps due to the presence of Alnus in the freshwater core, and Liriodendron tulipifera seeds found at the oligohaline marsh site, as well as Nyssa, Taxodium and Alnus pollen found at both sites. The accretion and accumulation rates are similar to the heavily salt-impacted site. Freshwater environments are characterized by low accretion and carbon accumulation. Higher accretion and carbon accumulation rates are found around 1700-1400 calibrated years before present, and can be seen in the cores with a decrease in hardwoods and increasing Nyssa, Taxodium, and Liriodendron evidence. The largest observed changes happened around 400 years ago, the same time of colonization and the increase in agriculture within the regions. The changes are marked in the cores by large increases in accretion, organic matter, and carbon accumulation. Another indicator of this is the increase of Poaceae, while evidence of Nyssa, hardwoods, and Taxodium diminish. Poaceae pollen and the presence of Scirpus and Carex seeds suggests a change to oligohaline marsh in relation to the increase of land use in the area. Reforestation efforts over the last 100 years show a decrease in accretion and carbon accumulation in all sites. The Savannah River cores were found to be roughly five to six thousand years old. The results from the cores along the Savannah River were found to be very similar to those from the Waccamaw River.
The study revealed that the same zones were also back swamps and that the freshwater core showed low accretion and carbon accumulation. The presence of Alnus designated this back swamp environment. Around 2,000 calibrated years before present, the sites show various changes in biota, but very little change in accretion and carbon accumulation rates. The largest change in the Savannah samples are found around 400 years ago, as was seen in the Waccamaw cores. All sites showed a decline in Nyssa, and an
increase in Poaceae, and what the researchers call weedier taxa, such as Scirpus, Sagittaria, and Polyganum. Both the Savannah River and the Waccamaw River both show stark increases in carbon accumulation and accretion rates right at the start of when colonization and agriculture increased in these regions dramatically, as well as when sea-level rise began to increase during the Holocene. The lowest accretion rates were found further inland, which is tied to an expansion of the marsh. Reforestation efforts coincided with lowered accretion rates, which increased the vulnerability with a rise in sea level. The tidal freshwater forested wetlands are vulnerable to the smallest of salinity changes.
Why this study is important? Wetlands like the ones studied in this research, are important for coastal communities because they help mitigate flooding and support many organisms, as well as fisheries, which provide millions of dollars in commercial and environmental goods and services. Wetlands are also important carbon sinks and help control the amount of CO2 in the atmosphere. Sea level rise today will affect these ecosystems and the people living near them. The results of this research are important for understanding the future long-term resilience of these ecosystems and what measures will be best suited to support these environments.
The big picture: The paper looked at evidence within sediment cores to understand the changes in carbon accumulation and accretion within two southeastern United States rivers. Core evidence indicated that there were increases in accretion and carbon accumulation rates with the emergence of colonization and agriculture in the area. Reforestation efforts in the last 100 years showed a decrease in accretion. The findings were then compared to sea level rise data to show that these environments become more vulnerable with increased sea level rises over the last 200-100 years. This research will be helpful in understanding the effects sea level rise in the future will have on this environment and the surrounding communities.
Citation: Jones, M. C., Bernhardt, C. E., Krauss, K. W., & Noe, G. B. (2017). The impact of late Holocene land use change, climate variability, and sea level rise on carbon storage in tidal freshwater wetlands on the southeastern United States coastal plain. Journal of Geophysical Research: Biogeosciences, 122(12), 3126–3141. https://doi.org/10.1002/2017jg004015

How global warming is changing the ecosystem in the Alps and Apennine Mountains

Assessment of climate change effects on mountain ecosystems through a cross-site analysis in the Alps and Apennines

Rogora M., Frate L., Carranza M.L., Freppaz M., Stanisci A., Bertani I., Bottarin R., Brambilla A., Canullo R., Carbognani M., Cerrato C., Chelli S., Cremonese E., Cutini M., DiMusciano M., Erschbamer B., Gogone D., Iocchi M., Isabellon M., Magnani A., Mazzola L., Morra di Cella U., Pauli H., Petey M., Petriccione B., Porro F., Psenner R., Rossetti G., Scotti A., Sommaruga R., Tappeiner U., Theurillat J.-P., Tomaselli M., Viglietti D., Viterbi R., Vittoz P., Winkler M., and Matteucci G.

Summarized by Agnes Wasielewski, who is an MAT Earth Science Graduate student at Binghamton University. She loves Geology so much that she decided to share her passion with middle and high school students by becoming a teacher. When she’s not studying Geology or the psychology of teenagers; she spends a lot of time with her husband, three children, and three dogs. When free time becomes available, she loves to read, hike, drink tea, and take naps with her dogs.

What data were used? Researchers collected data from twenty research sites across the Alps (Italy, Switzerland, and Austria) and Apennines Mountains (Italy). All sites were located between 1300 and 3212 meters above sea level. Fourteen sites are in forests, grasslands, alpine tundra, and snow-covered areas. Six sites are in lakes and rivers. All sites considered for the paper experienced an increase in air temperature over the past two decades (1991-2015) compared to a base period of 1961-1990. A combination of data analysis on already existing datasets, projects, and new collection of data to determine results.

Methods: Temperatures taken in June were used to determine snow melting rates, the timing of the beginning of the growing season, and timing of ice-break in lakes and rivers. To analyze regional snow cover duration, data loggers combined with thermistors (special resistors used  for temperature measurements) were placed at a soil depth of 10 cm and measured hourly. If the temperatures measured remained within a certain range, the day was considered a “snow cover day”. On days where the daily mean soil temperature dropped below and rose above 0 degrees Celsius, they were labeled as a freeze/thaw cycle. The snow melting date is identified by counting the days since October 1st to the start of the freeze/thaw cycle or melting period. Soil samples were collected in September at the end of the growing season and tests are run to determine water content, carbon content, and nitrate concentrations. 

Changes in vegetation cover were calculated by estimating the percentage of each plant species in permanent grids over time. These estimates are used as a proxy for above-ground biomass. Biomass is positive when vegetation cover increases and negative when cover decreases. 

Surface water samples for chemical analysis were obtained from lakes in late summer/early autumn. May to October is considered open water season, and water temperatures combined with chlorophyll-a concentrations and zooplankton abundance are recorded. Weather stations were used to collect average air temperatures. Biologic samples were analyzed from rivers at varying distances downriver of melting glaciers to correlate community composition and diversity.

Location of research sites where data was collected throughout the Alps and Apennine mountains in central and northern Italy, southern Switzerland, eastern and central Austria.
Location of research sites used for analysis within Italy, Switzerland, and Austria. Degree of temperature change from the baseline reflecting global warming.

Results: At lower altitudes (~1500 meters above sea level) and latitudes (Lat. 41 degrees N), there are shorter snow cover duration (less than 100 days/year) and snow starts to melt earlier in the year. At higher altitudes (~2800 meters above sea level) and latitudes (Lat. 46 degrees N), there are longer snow cover duration periods (~250 days) and snow starts to melt later in the year. Less snow-covered days allow for increased soil temperatures and more areas for plants to grow and thrive. When more plants can grow and thrive, there are more resources available to local wildlife such as the Alpine ibex (mountain goat) and helps support their population growth. Overall, increased air temperatures and soil temperatures showed a general tendency towards increased vegetation cover for treeline, subalpine, and alpine belts but not in the snow (nival) belts. Over the last fifteen years, it is noted that plant species have been migrating from lower elevations to higher elevations in a process called thermophilization.

An increase in nitrogen deposition has positive effects on tree growth and promotes carbon sequestration (the process of capturing and storing atmospheric carbon dioxide). However, reduction in rainfall can override the positive effects. In the forests tested, a significant increase in the growing season length and a general increase in the annual net carbon sequestration was detected.

During warm and dry years, alpine streams transport concentrated solutes into the lakes and in the runoff water. Over the past decade, there has been a common trend in decreasing nitrate concentrations. Nitrogen uptake in the lake catchments has increased due to the increase in primary productivity (algae and vegetation growth). There has an overall negative trend in NO3 concentration level in rivers and lakes due to decreasing Nitrogen deposition. 

Changes in water mineral and chemical concentrations also affect the diversity and population of algae and plankton that live and thrive in mountain lakes and streams.

Why is this study important? Climate warming effects, changes in rainfall seasonality, and water availability have proven to be important for ecosystem productivity. Snow cover duration affects soil carbon and nitrogen cycling and Alpine ibex population dynamics. Warming climate change has shown to lead to an increase in vegetation cover in grasslands and carbon uptake in forests which helps remove CO2 from the atmosphere. Climate drives changes in water chemistry, lake thermal dynamics and plankton phenology can inform us of the health of the water ecosystems. High-elevation ecosystems may also be affected by extreme climatic events such as heat waves, droughts, heavy rainfall, and floods. Both long-term and short-term (extreme) events can affect mountain ecosystems. Mountain ecosystems, if properly studied and monitored, can serve as early indicators of global changes.

The big picture: Global warming affects high mountain ecosystems by increases in temperature, early snowmelt, and a prolonged growing season. With ecosystem productivity, more plant growth helps reduce global climate change by reducing the amount of carbon dioxide in the atmosphere. In mountain ecosystems, carbon sequestration depends on both water availability (precipitation) and air temperature. The understanding of hydro-ecological relationships is essential for the development of effective conservation strategies for alpine rivers. Long-term observations on benthic communities help with the assessment of the potential impacts of global change on stream ecosystems. There is a great need for strong partnerships in mountain ecosystem observation and research for multidisciplinary approaches, encompassing the distinction between different types of ecosystems. There is great potential for further scientific advances that rely on international collaboration and integration.

Citation: Rogora, M., Frate, L., Carranza, M. L., Freppaz, M., Stanisci, A., Bertani, I., Bottarin, R., Brambilla, A., Canullo, R., Carbognani, M., Cerrato, C., Chelli, S., Cremonese, E., Cutini, M., Di Musciano, M., Erschbamer, B., Godone, D., Iocchi, M., Isabellon, M., … Matteucci, G. (2018). Assessment of climate change effects on mountain ecosystems through a cross-site analysis in the Alps and Apennines. The Science of the Total Environment624, 1429–1442. https://doi.org/10.1016/j.scitotenv.2017.12.155