Sequencing of Coastal Lagoon Samples from the Piñones Lagoon, Puerto Rico, Reveals Important Role of Bacterial Sulfur Metabolism in the Lagoon Ecosystem

Recent Nitrogen Storage and Accumulation Rates in Mangrove Soils Exceed Historic Rates in the Urbanized San Juan Bay Estuary (Puerto Rico, United States)

Tropical mangrove forests have been described as "coastal kidneys," promoting sediment deposition and filtering contaminants, including excess nutrients. Coastal areas throughout the world are experiencing increased human activities, resulting in altered geomorphology, hydrology, and nutrient inputs. To effectively manage and sustain coastal mangroves, it is important to understand nitrogen (N) storage and accumulation in systems where human activities are causing rapid changes in N inputs and cycling. We examined N storage and accumulation rates in recent (1970 - 2016) and historic (1930 - 1970) decades in the context of urbanization in the San Juan Bay Estuary (SJBE, Puerto Rico), using mangrove soil cores that were radiometrically dated. Local anthropogenic stressors can alter N storage rates in peri-urban mangrove systems either directly by increasing N soil fertility or indirectly by altering hydrology (e.g., dredging, filling, and canalization). Nitrogen accumulation rates were greater in recent decades than historic decades at Piñones Forest and Martin Peña East. Martin Peña East was characterized by high urbanization, and Piñones, by the least urbanization in the SJBE. The mangrove forest at Martin Peña East fringed a poorly drained canal and often received raw sewage inputs, with N accumulation rates ranging from 17.7 to 37.9 g -2 y-1 in recent decades. The Piñones Forest was isolated and had low flushing, possibly exacerbated by river damming, with N accumulation rates ranging from 18.6 to 24.2 g -2 y-1 in recent decades. Nearly all (96.3%) of the estuary-wide mangrove N (9.4 Mg ha-1) was stored in the soils with 7.1 Mg ha-1 sequestered during 1970-2017 (0-18 cm) and 2.3 Mg ha-1 during 1930-1970 (19-28 cm). Estuary-wide mangrove soil N accumulation rates were over twice as great in recent decades (0.18 ± 0.002 Mg ha-1y-1) than historically (0.08 ± 0.001 Mg ha-1y-1). Nitrogen accumulation rates in SJBE mangrove soils in recent times were twofold larger than the rate of human-consumed food N that is exported as wastewater (0.08 Mg ha-1 y-1), suggesting the potential for mangroves to sequester human-derived N. Conservation and effective management of mangrove forests and their surrounding watersheds in the Anthropocene are important for maintaining water quality in coastal communities throughout tropical regions.

The Eastern Nebraska Salt Marsh Microbiome Is Well Adapted to an Alkaline and Extreme Saline Environment

The Eastern Nebraska Salt Marshes contain a unique, alkaline, and saline wetland area that is a remnant of prehistoric oceans that once covered this area. The microbial composition of these salt marshes, identified by metagenomic sequencing, appears to be different from well-studied coastal salt marshes as it contains bacterial genera that have only been found in cold-adapted, alkaline, saline environments. For example, Rubribacterium was only isolated before from an Eastern Siberian soda lake, but appears to be one of the most abundant bacteria present at the time of sampling of the Eastern Nebraska Salt Marshes. Further enrichment, followed by genome sequencing and metagenomic binning, revealed the presence of several halophilic, alkalophilic bacteria that play important roles in sulfur and carbon cycling, as well as in nitrogen fixation within this ecosystem. Photosynthetic sulfur bacteria, belonging to Prosthecochloris and Marichromatium, and chemotrophic sulfur bacteria of the genera Sulfurimonas, Arcobacter, and Thiomicrospira produce valuable oxidized sulfur compounds for algal and plant growth, while alkaliphilic, sulfur-reducing bacteria belonging to Sulfurospirillum help balance the sulfur cycle. This metagenome-based study provides a baseline to understand the complex, but balanced, syntrophic microbial interactions that occur in this unique inland salt marsh environment.