Impact of groundwater table and plateau zokors (Myospalax baileyi) on ecosystem respiration in the Zoige Peatlands of China

Abstract

Peatlands contain large amount of carbon stock that is vulnerable to release into the atmosphere. Mostly because of human impact, the peatlands at Zoige Wetlands face severe degradation, and the groundwater table is now lower than before, which has increased the population of the plateau zokor, a burrowing rodent. However, the impact of these changes on ecosystem carbon flows has not been studied. To investigate how the plateau zokor and the groundwater level alter the ecosystem respiration of the Zoige peatlands, we sampled the CO2 flux of hummocks shaped by the zokors and compared it with the CO2 flux of undisturbed sites with different groundwater table levels. The soil organic carbon (SOC), soil water content (SWC) and soil temperature at 5 cm (T5) were measured. SOC showed no significant difference among the four sampling sites and did not correlate with the CO2 flux, while SWC was found to partly determine the CO2 flux. A linear equation could adequately describe the relationship between the natural logarithm of the ecosystem respiration and the soil temperature. It is demonstrated that descending groundwater table might accelerate ecosystem respiration and the CO2 flux from hummocks was higher than the CO2 flux from the control site in the non-growing season. With rising temperature, the CO2 flux from the control site accelerated faster than that from the hummocks. Our results show that ecosystem respiration was significantly lower from hummocks than at the control site in the growing season. The results on the impact of zokors on greenhouse gas emissions presented in this paper provide a useful reference to help properly manage not only this, but other litter-burrowing mammals at peatland sites.

Figure 1. Distribution of the study sites in the Zoige peatland.

The three study plots (LIT, INT and ZOK) are shown by black dots. The distance from plot ZOK (33.929°N, 102.820°E; 3439m a.s.l.) to plot INT (33.923°N, 102.817°E; 3437m a.s.l.) is approximately 700 m, and the distance from plot INT to plot LIT (33.918°N, 102.818°E; 3435m a.s.l.) is approximately 600 m. Six permanent samples were taken each time, and are marked by solid triangle at each plot, and named as LIT, INT and CON, whereas for sample HUM, six samples were taken each time, and then, move to another location to take second, and third sets of samples, which are marked by open triangle at plot ZOK. The image at left bottom shows the border line of the Zoige County and the Zoige National Nature Reserve. The blue area in the right image represents Huahu Lake, whilst plateau zokor aggregates in the area above the dot line.

Figure 2. PVC tube place over the plateau zokor hummocks in the Zoige peatlands.

Figure 3. SOC (mean ± SE) compared among the sites at three depth layers.

Comparison of SOC in the 0–10, 10–20 and 20–30 cm layers among the four sites. Within the same layer group, the SOC values with the same lowercase letter do not differ significantly (P>0.05) based on the Dunn's multiple comparison test.

Figure 4. Diurnal CO₂ flux from the four sites in 2012.

The diurnal dynamics of CO₂ flux from the four sites were collected in June, July and October 2012.

Figure 5. Correlation between ecosystem respiration and T₅ each groundwater table treatment, as well as for plateau zokor treatment.

A linear equation describing the correlation between the natural logarithm of the ecosystem respiration and the soil temperature and the 95% confidence interval are shown: site LIT (y = 0.11x+0.33, R ² = 0.83, P<0.001); site INT (y = 0.10x+0.83, R ² = 0.68, P<0.001); site CON (y = 0.10x+0.92, R ² = 0.77, P<0.001); site HUM (y = 0.04x+1.13, R ² = 0.46, P<0.001).