Roundup: Decaying Matter, Glacial Bacteria, and CO2 Uptake

Transport of Nutrients and Decaying Matter by Rivers and Streams

From “Intermittent Rivers and Ephemeral Streams”: “The hydrological regimes of most intermittent rivers and ephemeral streams (IRES) include the alternation of wet and dry phases in the stream channel and highly dynamic lateral, vertical, and longitudinal connections with their adjacent ecosystems. Consequently, IRES show a unique ‘biogeochemical heartbeat’ with pulsed temporal and spatial variation in nutrient and organic matter inputs, in-stream processing, and downstream transport. Given that IRES are widespread, their improper consideration may cause inaccurate estimation of nutrient and carbon fluxes in river networks… Our purpose is to contribute to the flourishing knowledge and research on the biogeochemistry of IRES by providing a comprehensive view of nutrient and organic matter dynamics in these ecosystems.”

Read more about the findings here.

Photo of intermittent river in Boliva
An intermittent river in Bolivia (Source: Thibault Datry‏/Twitter).

 

Glacial Bacteria Originated on Slopes Near Alaskan Glacier

From Microbiology Ecology: “Although microbial communities from many glacial environments have been analyzed, microbes living in the debris atop debris-covered glaciers represent an understudied frontier in the cryosphere. The few previous molecular studies of microbes in supraglacial debris have either had limited phylogenetic resolution, limited spatial resolution (e.g. only one sample site on the glacier) or both. Here, we present the microbiome of a debris-covered glacier across all three domains of life, using a spatially-explicit sampling scheme to characterize the Middle Fork Toklat Glacier’s microbiome from its terminus to sites high on the glacier. Our results show that microbial communities differ across the supraglacial transect, but surprisingly these communities are strongly spatially autocorrelated, suggesting the presence of a supraglacial chronosequence… We use these data to refute the hypothesis that the inhabitants of the glacier are randomly deposited atmospheric microbes, and to provide evidence that succession from a predominantly photosynthetic to a more heterotrophic community is occurring on the glacier.”

Learn more about glacial bacteria here.

Topographic map of bacteria sample sites
Topographic map of bacteria sample sites on the Middle Fork Toklat Glacier (Source: Darcy et al.).

 

Simulated High Alkalinity Glacial Runoff Increases CO2 Uptake in Alaska

From Geophysical Research Letters: “The Gulf of Alaska (GOA) receives substantial summer freshwater runoff from glacial meltwater. The alkalinity of this runoff is highly dependent on the glacial source and can modify the coastal carbon cycle. We use a regional ocean biogeochemical model to simulate CO2 uptake in the GOA under different alkalinity-loading scenarios. The GOA is identified as a current net sink of carbon, though low-alkalinity tidewater glacial runoff suppresses summer coastal carbon uptake. Our model shows that increasing the alkalinity generates an increase in annual CO2 uptake of 1.9–2.7 TgC/yr. This transition is comparable to a projected change in glacial runoff composition (i.e., from tidewater to land-terminating) due to continued climate warming. Our results demonstrate an important local carbon-climate feedback that can significantly increase coastal carbon uptake via enhanced air-sea exchange, with potential implications to the coastal ecosystems in glaciated areas around the world.”

Read more about the study here.

Photo of the Gulf of Alaska from space
The Gulf of Alaska from space (Source: NASA Goddard Images/Twitter).

 

Glacier Melting Sets Free Organic Carbon

Research has shown that glaciers have a greater role than was previously known in the movement of organic carbon into and through aquatic ecosystems, including the oceans. Organic Carbon (OC) refers to carbon contained in organic compounds that is originally derived from decaying vegetation, bacterial growth, and metabolic activities of living organisms. It serves as a primary food source for marine organisms, particularly microbes. In addition, it contributes to the acidification of water. Particularly in freshwater ecosystems, excessive OC can result in a brownish coloration. In fact, the amount of OC is often used as an indicator of overall water quality.

Figure 1. Location of glacier DOC samples classified by type. a–d, Samples were collected from a wide variety of glacial environments including: Alaska (a), Tibet (b), Dry Valley glaciers in Antarctica (c), and the Greenland Ice Sheet (d). (Source: Hood et al.)
Figure 1. Location of glacier DOC samples classified by type. a–d, Samples were collected from a wide variety of glacial environments including: Alaska (a), Tibet (b), Dry Valley glaciers in Antarctica (c), and the Greenland Ice Sheet (d). (Source: Hood et al.)

A recent research shows that the increase in glacier runoff through melting and iceberg calving has led to a rise of OC flux entering marine and lacustrine ecosystems, and this flux is expected to grow in the coming decades. According to the article, glacier ecosystems accumulate OC from primary production on the glacier surface, particularly in cryoconite deposits, and also from the deposition of carbonaceous material derived from terrestrial and anthropogenic sources.

To quantify the total storage of OC in terrestrial ice reservoirs, the study integrates measurements of organic carbon from mountain glaciers, ice sheets in Greenland, and Antarctica Ice Sheet, with data from locations that span five continents (see Figure 1). It turns out that that largest amount of OC is located in Antarctica, followed by Greenland and mountain glaciers. However, it is found in the study that a large portion of the OC released from melting glaciers is from mountain glaciers and peripheral glaciers which exit from the Greenland ice sheets (see Figure 2). The surprisingly disproportionately high DOC export from mountain glaciers and Greenland is associated with their glacier mass turnover rate, which is higher than in Antarctica. Even as glaciers are losing ice through melting and caving at their lower ends, they continue to receive new snow at the top, which converts to ice—a process of flow, which contributes to the movement of OC through the glaciers.

Figure 2. Storage and flux of glacier DOC. Total glacier storage of DOC (a) and annual DOC export in glacier runoff (b) for MGL, GIS, and AIS.
Figure 2. Storage and flux of glacier DOC. Total glacier storage of DOC (a) and annual DOC export in glacier runoff (b) for AIS (Antarctic Icesheet), GIS (Greenland Icesheet) and MGL (mountain glaciers). (Source: Hood et al.)

Dissolved organic carbon (DOC) and particulate organic carbon (POC), two major components of the OC, are both significant components in the carbon cycle, because they are primary food sources in aquatic food webs. In particular, DOC forms complexes with trace metals, which can be transported and consumed by organisms. This may have drastic affects on marine life, “because this material is readily consumed by microbes at the bottom of the food chain,” said U.S. Geological Survey research glaciologist and co-author of the research Shad O’Neel. The microbes are an important source of food for plankton and for larger organisms in the seas, including crustaceans and fish.

 

Iceberg Calving (Source: Flickr/Indistinct)
Iceberg Calving (Source: indistinct/Flickr)

The study raises questions of the implications of OC input for carbon dioxide concentration in atmosphere. The authors suggest that glacier-derived OC shows a high degree of biological availability, when compared to other terrestrial sources. Hence, it is more likely to result in more rapid decomposition of dead marine organisms, which otherwise would fall from upper zones of the oceans to deeper sections, where they would remain for long periods. This decomposition, in turn, contributes to carbon dioxide outgassing from the oceans to the atmosphere.

For another story about the effects of glaciers on ocean chemistry and ecology, look here.