Water Quality Monitoring

Freshwater and marine water quality research is carried out by TIDE at 43 sites in the Maya Mountain Marine Corridor (27 within Port Honduras Marine Reserve (PHMR), 7 in Monkey River and 7 in Rio Grande) in order to understand the health of water systems between the land and sea at the landscape scale. This program involves a collaborative, integrated approach by the terrestrial fieldwork team headed by Elmar Requena and the marine fieldwork team headed by Tanya Barona, with overall project management and integrated data analysis and reporting carried out by James Foley, TIDE science director.

 

TIDE has been monitoring water quality at various sites with varying levels of continuity since 1998, but in 2011 a large effort was made to expand the monitoring effort, standardize sampling methods and integrate the marine and freshwater programs into one overarching water quality monitoring program. Freshwater river systems are inextricably linked to marine waters since rivers flow into the ocean, and monitoring marine and freshwater as one connected system can help us to understand more completely the impacts terrigenous runoff have on marine ecosystems. Monkey River and Rio Grande both empty into the waters of PHMR, so a comprehensive monitoring program that includes all three systems can reveal much about the interconnectivity between them and facilitate better management of protected areas.

TIDE now regularly monitors all sites, recording temperature, salinity (the amount of salt in the water), dissolved oxygen (the amount of oxygen in the water), pH (the level of acidity), sedimentation (how particles suspended in the water settle out on the bottom), nutrients (phosphates and nitrates, which feed plant life, the basis of the food chain), turbidity (the cloudiness of the water) and visibility on monthly trips.  The water quality indicators we monitor are very important for the life living in these marine and freshwater systems and all dictate what lives where in an ecosystem. By observing these factors, researchers can ascertain the health of the water systems throughout the year.

Results:

Temperature changes can have a huge effect on the organisms living within river systems and the ocean.  During this study it was found that between 2009 and 2015, mean surface temperature was generally coolest between November and January, then increased steadily until April. In general, PHMR is warmer than the rivers, however PHMR’s mean overall surface temperature has declined since 2009, with the exceptions of 2011 and 2015. Although we are not certain why this is occurring, some possible causes include increased rainfall and cloud cover within the Maya Marine Mountain Corridor (MMMC) due to climate change.

Salinity also influences life in the water since most organisms can only tolerate a particular salinity range. Salinity in PHMR fluctuates with inputs of freshwater from rain and river discharge, which reduce salinity, but these effects are largest at the water’s surface and near river mouths. Seasonal trends in salinity, influenced by rainfall patterns, have remained fairly constant during the course of our study.

Like temperature and salinity, pH also plays a role in where organisms live in aquatic ecosystems. In general, saltwater usually has a higher pH (less acidic, or more alkaline) whereas freshwater tends to be more neutral. Therefore, pH is usually lower (more neutral) in the upper streams of the Monkey River and Rio Grande river systems than at the mouths of the rivers and in PHMR. During times of high rainfall and increased river flow, however, pH in PHMR decreases near the rivers’ mouths.

Having the right amount of dissolved oxygen (DO) in a water body is essential for a healthy ecosystem. Photosynthesizing plant life in the water produce oxygen and many organisms depend on it. Having enough DO is crucial for aquatic life; however, too much DO in surface waters can be a sign of excess nutrients entering the water from agricultural and household runoff, which can cause an overgrowth in the microscopic waterborne algae that consume them. These algae blooms at the surface cloud the water, preventing light from reaching plant life on the sea floor. Then, when all the algae die off and sink, they are decomposed by bacteria that consume oxygen, which can result in dead zones where there is not enough oxygen to sustain life. Our 2015 data reveal that DO in all areas tended to be highest in the beginning and end of the year. No consistent trends in DO have been observed from year to year as of yet, however.

Household and agricultural wastes produce nitrate and phosphate, nutrients that plant life consume to grow. During rainy seasons, increased runoff from the land carries these excess nutrients into waterways, potentially causing harmful overgrowth. Higher concentrations of nutrients in parts of Monkey River and Rio Grande in 2015 suggest increased human impact, particularly from agriculture. Runoff that enters Monkey River and Rio Grande will eventually be introduced into PHMR. The white sediment plumes visible from the river mouths in the below satellite image of PHMR and the surrounding watersheds demonstrates how far water from rivers, along with the sediments and nutrients it carries, is transported along the coast and the high potential to impact PHMR waters.

Sedimentation indicates the amount of and the rate at which sand and silt are deposited in rivers and oceans. High sedimentation rates can be harmful to important sea floor ecosystems like coral reefs and seagrass beds, which provide habitat and food for many ecologically and commercially significant species. Sedimentation rates tend to be highest in the beginning of the wet season, as the first rains wash out all the sediments that have accumulated throughout the dry season. Sedimentation is often linked to visibility as it causes the water to appear murky. The murkiness caused by sediments suspended in the water column is what we measure when we monitor turbidity, an increase of which will limit visibility in the water. Overall there is not an obvious trend in visibility over each year from 2009-2015. Visibility is influenced by many different factors that can cause daily fluctuations, but the general trend is that visibility increases further from the shore, except during periods of high river discharge, rainfall or wind.

Current research (2015)

TIDE’s water quality monitoring research has been running since 2009, and monthly monitoring trips continue. Each year a report is compiled, comparing annual data from Monkey River, Rio Grande and PHMR in order to understand how seasonal changes in these rivers affect conditions in PHMR. An important part of TIDE’s water quality monitoring is to determine causes and effects of reduced water quality. By understanding threats in MMMC’s water systems, TIDE is able to make recommendations for stakeholders and can better manage the river catchments in TIDE’s terrestrial protected areas and the ecological and fisheries resources in PHMR.

To help strengthen interpretation of the data, habitat mapping was begun in 2014 and this will aid our understanding of coastal marine benthic structure, influence of habitat type on water quality, water circulation patterns and impacts of river runoff on coastal environments. The animated map below shows changes in visibility, an important indicator for water quality, at our monitoring sites throughout the year.

For a full review of water quality in Monkey River, Rio Grande and Port Honduras Marine Reserve, read our annual integrated water quality report, available for download below.

TIDE WQM 2013 FINAL REPORT Foley

TIDE WQM 2014 ANNUAL REPORT_Foley

TIDE WQM 2015 ANNUAL REPORT Foley

Integrating climate change into the TIDE freshwater programme