Although plastic pollution happens globally, the micro- (<5 mm) and macroplastic (5–150 mm) transfer of plastic to terrestrial species relevant to human consumption has not been examined. We provide first-time evidence for micro- and macroplastic transfer from soil to chickens in traditional Mayan home gardens in Southeast Mexico where waste mismanagement is common. We assessed micro- and macroplastic in soil, earthworm casts, chicken feces, crops and gizzards (used for human consumption). Microplastic concentrations increased from soil (0.87 ± 1.9 particles g−1), to earthworm casts (14.8 ± 28.8 particles g−1), to chicken feces (129.8 ± 82.3 particles g−1). Chicken gizzards contained 10.2 ± 13.8 microplastic particles, while no microplastic was found in crops. An average of 45.82 ± 42.6 macroplastic particles were found per gizzard and 11 ± 15.3 macroplastic particles per crop, with 1–10 mm particles being significantly more abundant per gizzard (31.8 ± 27.27 particles) compared to the crop (1 ± 2.2 particles). The data show that micro- and macroplastic are capable of entering terrestrial food webs.
/ We present results of a study in an intensively impacted and highly fragmented landscape in which we apply field-measured carbon (C) density values to land-use/land-cover (LU/LC) statistics to estimate the flux of C between terrestrial ecosystems and the atmosphere from the 1970s and 1990s. Carbon densities were assigned to common LU/LC classes on vegetation maps produced by Mexican governmental organizations and, by differencing areas and C pools, net C flux was calculated from the central highlands of Chiapas, Mexico, during a 16-year period. The total area of closed forests was reduced by half while degraded and fragmented forests expanded 56% and cultivated land and pasture areas increased by 8% and 30%, respectively. Total mean C densities ranged from a high of 504 tons C/ha in the oak and evergreen cloud forests class to a low of 147 tons C/ha in the pasture class. The differences in total C densities among the various LU/LC classes were due to changes in biomass while soil organic matter C remained similar. We estimate that a total of 19.99 thick similar 10(6) tons C were released to the atmosphere during the period of time covered by our study, equal to approximately 34% of the 1975 vegetation C pool. The Chiapas highlands, while comprising just 0.3% of Mexico's surface area, contributed 3% of the net national C emissions. KEY WORDS: Land use; Land cover; Carbon flux; Forests; Chiapas highlands; Mexico
Forest conversion to agriculture and grassland has been widespread in south-eastern Mexico. The productivity, functioning and carbon dynamics of secondary forests growing after abandonment of agricultural fields are expected to differ from those of primary forests. This study analysed whether forest age and seasonal variations affect the amount and temporal distribution of litterfall and associated nutrient transfer. Litterfall was measured across a chronosequence of semi-evergreen tropical forest in Calakmul, Yucatan peninsula, Mexico, and an index was created to evaluate the effect of land use intensity on litterfall collected in 16 stands from October 2012 to September 2014. Total litterfall ranged from 5.2 ± 0.6 to 7.1 ± 0.3 Mg ha -1 year -1 and peaked in secondary forest aged 10-20 years. Leaves contributed 84-91 % of total litterfall. The associated transfer of carbon ranged from 2.3 ± 0.3 to 3.2 ± 0.1 Mg ha -1 year -1 and of nitrogen from 62 ± 7 to 84 ± 4 kg ha -1 year -1 . Carbon and nutrient accumulation in the organic horizon (Oa) increased significantly with forest age. However, carbon in mineral soil (down to 0.30 m depth) did not increase over time. Peaks in monthly litterfall coincided with the dry season, with higher peaks in a year with lower rainfall in the dry season. Peaks were also higher in secondary forests than in primary forests, due to changes in species composition. Higher land use intensity reduced carbon and nutrient transfer through litter in regenerating secondary forests. Longer-term research is required to analyse the climate sensitivity of litter dynamics in these tropical forest frontiers.
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