Freshwater and Marine water quality research is carried out by TIDE at 48 sites within Port Honduras Marine Reserve (PHMR), Monkey River and Rio Grande in order to understand the health of water systems between the land and sea in the Maya Mountain Marine Corridor (MMMC). This program involves a collaborative, integrated approach using 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.
Research has been running from 2009 to 2014 to compare the annual data of two rivers named Rio Grande and Monkey River and also PHMR. Both these rivers run into PHMR and its barrier reef system so it is integral to understand how seasonal changes in these rivers affect conditions in PHMR. By understanding threats in MMMC’s water systems, TIDE is able to make recommendations for stakeholders, fishers and can better manage the river catchments and reserve.
The research monitors salinity, dissolved oxygen, sedimentation, temperature, phosphates, nitrates, turbidity and visibility on monthly trips. By observing these factors, researchers can ascertain the health of the water systems throughout the year.
Temperature can have a huge affect on the organisms living within river systems and the ocean. During this study it was found that between 2009 and 2013, mean surface temperature was generally cool in January (26.8°C) and then increased steadily to between 29.3°C to 30.5°C by April. In general, PHMR is warmer than the rivers, however PHMR’s mean overall surface temperature has declined since 2009, with the exception of 2011, although we are not certain why this is occurring. Results have also shown the warming period has peaked later in 2013 than 2012.
Dissolved oxygen (DO) is the amount of oxygen present in a water body and it is measured in percentage (%) and mg/l. In 2013, DO was higher in inland areas during warmer months, which suggests impacts from agriculture in this area, such as increased nutrients present and increased plant cover. However, levels tend to recover downstream, suggesting the impact of farming is fairly localized. Lowest DO was seen in November and this could be due to high levels of sedimentation being washed into the river from the land. Consequently, this sediment then washes into the northern half of PHMR.
Household and agricultural waste produces nitrate and phosphate and these substances were in general highest in November in PHMR, as this coincides with drier conditions when there is less water and thus higher concentrations of chemical and organic waste. However, in the rainy season, land run-off is more likely to reach the river due to the high level of water joining streams. High nitrate and phosphate together is more indicative of agricultural runoff, whereas high phosphate alone would be more indicative of domestic waste. There appears to have been an increase in phosphates in Rio Grande since 2012 and this could be due to population increase in areas along the Rio Grande watershed. The image below shows the high level of run off from the land and how far it spreads out into the surrounding coastline.
Sedimentation indicates the amount of sand and silt deposited in rivers and oceans. Sedimentation rates are highest between February and June, but drop off between September and December in both marine and freshwater environments. Sedimentation is often linked to visibility as it causes the water to appear murky. Overall there is not an obvious trend in visibility over each year from 2009-2013. The general trend is that visibility increases further from the shore, with offshore visibility worsening and becoming more like inshore areas during periods of high river discharge, rainfall or wind.
Current research (2014)
An important part of TIDE’s water quality monitoring is to determine causes of reduced quality water systems. To help strengthen interpretation of the data, habitat mapping was used 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.
Animated water quality visibility 2014