ABSTRACT. Urban activities and related infrastructure alter the natural patterns of stream physical and chemical conditions. According to the Urban Stream Syndrome, streams draining urban landscapes are characterized by high concentrations of nutrients and ions, and might have elevated water temperatures and variable oxygen concentrations. Here, we report temporal and spatial variability in stream physicochemistry in a highly urbanized watershed in Puerto Rico. The main objective of the study was to describe stream physicochemical characteristics and relate them to urban intensity, e.g., percent impervious surface cover, and watershed infrastructure, e.g., road and pipe densities. The Río Piedras Watershed in the San Juan Metropolitan Area, Puerto Rico, is one of the most urbanized regions on the island. The Río Piedras presented high solute concentrations that were related to watershed factors, such as percent impervious cover. Temporal variability in ion concentrations lacked seasonality, as did all other parameters measured except water temperature, which was lower during winter and highest during summer, as expected based on latitude. Spatially, stream physicochemistry was strongly related to watershed percent impervious cover and also to the density of urban infrastructure, e.g., roads, pipe, and building densities. Although the watershed is serviced by a sewage collection system, illegal discharges and leaky infrastructure are probably responsible for the elevated ion concentration found. Overall, the Río Piedras is an example of the response of a tropical urban watershed after major sewage inputs are removed, thus highlighting the importance of proper infrastructure maintenance and management of runoff to control ion concentrations in tropical streams.

ABSTRACT. Green areas, also known as green infrastructure or urban vegetation, are vital to urbanites for their critical roles in mitigating urban heat island effects and climate change and for their provision of multiple ecosystem services and aesthetics. Here, I provide a high spatial resolution snapshot of the green cover distribution of the city of San Juan, Puerto Rico, by incorporating the use of morphological spatial pattern analysis (MSPA) as a tool to describe the spatial pattern and connectivity of the city's urban green areas. Analysis of a previously developed IKONOS 4-m spatial resolution classification of the city of San Juan from 2002 revealed a larger area of vegetation (green areas or green infrastructure) than previously estimated by moderate spatial resolution imagery. The city as a whole had approximately 42% green cover and 55% impervious surfaces. Although the city appeared greener in its southern upland sector compared to the northern coastal section, where most built-up urban areas occurred (66% impervious surfaces), northern San Juan had 677 ha more green area cover dispersed across the city than the southern component. MSPA revealed that most forest cover occurred as edges and cores, and green areas were most commonly forest cores, with larger predominance in the southern sector of the municipality. In dense, built-up, urban land, most of the green areas occurred in private yards as islets. When compared to other cities across the United States, San Juan was most similar in green cover features to Boston, Massachusetts, and Miami, Florida. Per capita green space for San Juan (122.2 m²/inhabitant) was also comparable to these two U.S. cities. This study explores the intra-urban vegetation variation in the city of San Juan, which is generally overlooked by moderate spatial resolution classifications in Puerto Rico. It serves as a starting point for green infrastructure mapping and landscape pattern analysis of the urban green spaces within the city of San Juan. The effectiveness of research and city planning will be further enhanced as a result of this type of finer-scale urban cover exploration.

Fine-scale information about urban vegetation and social-ecological relationships is crucial to inform both urban planning and ecological research, and high spatial resolution imagery is a valuable tool for assessing urban areas. However, urban ecology and remote sensing have largely focused on cities in temperate zones. Our goal was to characterize urban vegetation cover with sub-meter (<1 m) resolution aerial imagery, and identify social-ecological relationships of urban vegetation patterns in a tropical city, the San Juan Metropolitan Area, Puerto Rico. Our specific objectives were to (1) map vegetation cover using sub-meter spatial resolution (0.3-m) imagery, (2) quantify the amount of residential and non-residential vegetation, and (3) investigate the relationship between patterns of urban vegetation vs. socioeconomic and environmental factors. We found that 61% of the San Juan Metropolitan Area was green and that our combination of high spatial resolution imagery and object-based classification was highly successful for extracting vegetation cover in a moist tropical city (97% accuracy). In addition, simple spatial pattern analysis allowed us to separate residential from non-residential vegetation with 76% accuracy, and patterns of residential and non-residential vegetation varied greatly across the city. Both socioeconomic (e.g., population density, building age, detached homes) and environmental variables (e.g., topography) were important in explaining variations in vegetation cover in our spatial regression models. However, important socioeconomic drivers found in cities in temperate zones, such as income and home value, were not important in San Juan. Climatic and cultural differences between tropical and temperate cities may result in different social-ecological relationships. Our study provides novel information for local land use planners, highlights the value of high spatial resolution remote sensing data to advance ecological research and urban planning in tropical cities, and emphasizes the need for more studies in tropical cities.

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