Luquillo LTER

Long-term Research Benefits Puerto Rico Water Management

The long-term ecological information needed to evaluate and manage natural resources is commonly not available to local regulatory agencies. This is especially true for water diversions, which often are designed for decades of service. At the Luquillo site, LTER data has been used to assess the impacts of water diversions on aquatic organisms and help local and Federal environmental regulatory agencies develop plans to mitigate adverse impacts.

When it became apparent to the regulatory agencies that these water diversions are often over designed, resulting in the reduction of abundance and biodiversity of aquatic organisms, long-term ecological studies from the Luquillo site were consulted. Specifically, LTER-data has been used by engineers to develop long-term hydrologic budgets and determine the frequency and impacts of droughts and floods on specific projects, including a $60 million dam and several $10 million water intakes. Data from the long-term monitoring of the dominant aquatic species and life history information collected by LTER graduate students also have been used in a collaborative effort among LTER scientists, the local water authority, and U.S. Forest Service and U.S. Fish and Wildlife Service managers to determine the stream flows and habitat requirements to needed to maintain their populations. As a direct result of these efforts, the Puerto Rican Water company and local and Federal environmental regulatory agencies now use instream flows standards based on Luquillo LTER data. LTER-collected data on the migration of aquatic organisms has also been used to design new water intakes and develop water extraction schedules that reduce impacts in existing water intakes. Using this basic ecological information, the mortality of larval organisms that migrate past these intakes can be reduced from 70% or more to less than 20% with a cost of less than a 5% in extracted water.

Humans are the strongest disturbance, even in hurricane-dominated system

An ecosystem is a historical construction, largely shaped by the legacies of past events (Margalef 1969). Research in the LUQ LTER clearly illustrates this point.

In 1990 LUQ LTER established a 16-ha forest study area in which all trees greater than 1 cm diameter are marked, mapped, measured and identified every five years. In this tropical forest, characterized by year-round growth, frequent damaging hurricanes, and steep topographic and soil variation, we found that it was history, in the form of long-abandoned land uses, not the other very strong influences, that has the biggest effect on present-day tree species composition. Figure 1 shows the forest conditions a surveyor recorded in 1934 along transect lines in the vicinity of the future 16-ha plot (Thompson et al. 2002). The forest in the north of the area had been heavily logged or cleared. The forest in the south had been lightly selectively logged. In the 70 years since, there have been several damaging hurricanes but no further human disturbance. Figure 2 shows the legacy of the human impacts. The much-disturbed north of the 16-ha plot is now dominated by the tree Casearia arborea, while the little-disturbed south is dominated by Dacryodes excelsa. More detailed, quantitative analyses using all 90 species of large trees on the 16-ha plot confirm that history has affected species composition more than violent natural disturbance and other strong site-factors have.