Variability in organic carbon reactivity across lake residence time and trophic gradients

The transport of dissolved organic carbon from land to ocean is a large dynamic component of the global carbon cycle. Inland waters are hotspots for organic matter turnover, via both biological and photochemical processes, and mediate carbon transfer between land, oceans and atmosphere. However, predicting dissolved organic carbon reactivity remains problematic. Here we present in situ dissolved organic carbon budget data from 82 predominantly European and North American water bodies with varying nutrient concentrations and water residence times ranging from one week to 700 years. We find that trophic status strongly regulates whether water bodies act as net dissolved organic carbon sources or sinks, and that rates of both dissolved organic carbon production and consumption can be predicted from water residence time. Our results suggest a dominant role of rapid light-driven removal in water bodies with a short water residence time, whereas in water bodies with longer residence times, slower biotic production and consumption processes are dominant and counterbalance one another. Eutrophication caused lakes to transition from sinks to sources of dissolved organic carbon. We conclude that rates and locations of dissolved organic carbon processing and associated CO2 emissions in inland waters may be misrepresented in global carbon budgets if temporal and spatial reactivity gradients are not accounted for

Maternal Neuroendocrine Serum Levels in Exclusively Breastfeeding Mothers

Background: Low milk supply is a common cause of early weaning, and supply issues are associated with dysregulation of thyroid function and prolactin. However, hormone levels compatible with successful breastfeeding are not well defined, limiting interpretation of clinical lab results. In this study we sought to quantify ranges for thyroid-stimulating hormone (TSH), free thyroxine (T4), total T4, and prolactin in a cohort of exclusively breastfeeding women. Materials and Methods: Women planning to breastfeed were recruited in the third trimester of pregnancy. Maternal endocrine function was assessed before and after a breastfeeding session at 2 and 8 weeks postpartum. We used paired t tests to determine whether values changed from the 2- to 8-week visit. Results: Of 52 study participants, 28 were exclusively breastfeeding, defined as only breastmilk feeds in the prior 7 days, at both the 2- and 8-week study visits. Endocrine function changed with time since delivery: the TSH level was higher, whereas total T4, free T4, and prolactin levels were lower, at the 8-week visit than at the 2-week visit (by paired t test, p≤0.01). We found a wide range of prolactin values at the 8-week visit, with a 5th percentile value of 9 ng/dL before feeding and 74 ng/dL at 10 minutes after feeding. Conclusions: Neuroendocrine function changes during the first 8 weeks after birth, and a wide range of values is compatible with successful breastfeeding. Further studies are needed to define reference values in breastfeeding women