Since underwater acoustic (UWA) networks have the nature of long propagation delay, low bit rates and error-prone acoustic communication, protocols designed for underwater acoustic networks are significantly different from that of terrestrial radio networks. Limited by these nature of UWA channels, conventional medium access control (MAC) protocols of radio packet network ether have low efficiency or are not able to apply to underwater acoustic networks. It is necessary to develop an efficient MAC protocol for underwater acoustic networks. In this paper, a collision-free MAC protocol for UWA networks called Ordered Carrier Sense Multiple Access (Ordered CSMA) is proposed and analyzed. Ordered CSMA combines the concepts of round-robin scheduling and CSMA. In Ordered CSMA, each station transmits data frame in a fixed order. More specifically, each station transmits immediately after the data frame transmission of last station in the order, instead of waiting for a period of maximum propagation delay. To achieve this, each station is constantly sensing the carrier and listens to all received frames. Due to the characteristics of collision free and high channel utilization, Ordered CSMA shows a great MAC efficiency improvement in our simulations, compared to previous works.

Widespread soil acidification due to atmospheric acid deposition and agricultural fertilization may greatly accelerate soil carbonate dissolution and CO2 release. However, to date, few studies have addressed these processes. Here, we use meta-analysis and nationwide-survey datasets to investigate changes in the soil inorganic carbon (SIC) stocks in China. We observe an overall decrease in the SIC stocks in topsoil (0-30 cm) (11.33 g C m–2 yr–1) during the 1980 s and 2010 s. The total SIC stocks have decreased by approximately 8.99 ± 2.24% (1.37 ± 0.37 Pg C). The average SIC losses across China (0.046 Pg C yr–1) and in cropland (0.016 Pg C yr–1) account for approximately 17.6–24.0% of the terrestrial C sink and 57.1% of the soil organic carbon sink in cropland, respectively. Nitrogen deposition and climate change have profound influences on SIC cycling. We estimate that approximately 19.12–19.47% of the SIC stocks will be further lost by 2100. The consumption of SIC may offset a large portion of the global efforts aimed at ecosystem carbon sequestration, which emphasizes the importance of better understanding the indirect coupling mechanisms of nitrogen and carbon cycling and of effective countermeasures to minimize SIC loss.

Protecting and improving cultivated land quality is a key way to the realization of agricultural modernization. The Chinese government advocates agricultural producers to implement cultivated land protection and quality improvement behavior (CLPQIB). However, the cultivated land management rights of family farms are not so stable. In order to study how stability of land management rights (SLMR) affects family farms’ CLQPIB, promoting family farms in adopting technologies to protect cultivated land, this study investigated 117 family farms in Anhui and Hubei provinces by stratified sampling and analyzed data through the logistic regression model and marginal effects model. The results showed that transferred land ratio, contract types, and contract duration affected family farms’ CLPQIB significantly. The probability of family farms applying organic fertilizer decreased by 0.9% for every 1% increase of the transferred land ratio. Family farms’ rented land through formal contracts have a 21.4% higher probability of adopting planting–breeding technology than family farms’ rented land through informal contracts. For every additional year of the rental contract duration, the possibility for family farms to replace chemical fertilizer with organic fertilizer, pesticides reduction, and integrated planting-breeding increase by 2.1%, 2.2%, and 1.3%, respectively. The results of this study can guide policy makers with further regulating land transfer behavior, guide family farms with signing formal lease contracts, and extending the duration of lease contracts, improving the cultivated land protection behavior of family farms.