ESSCOSMOS/2009:FieldSampling

Overview

The present activity applies classroom study of photosynthesis and decomposition to the modern challenge of calculating the effects of human impacts on ecosystem function. School, community, and other urban gardens provide an opportunity to explore the effects that humans can have on these fundamental biological processes.

Gardens are ecosystems that are managed by humans to optimize food production. With respect to photosynthesis and decomposition, gardens function much differently from surrounding grasslands and coastal sage shrub ecosystems. Humans increase the supply of water and nutrients to plants. At the same time, pesticides, weed removal, and crop planting alter the number and identity of plant and insect species.

Figure 7.3. The global carbon cycle for the 1990s, showing the main annual fluxes in GtC yr–1: pre-industrial ‘natural’ fluxes in black and ‘anthropogenic’ fluxes in red (modified from Sarmiento and Gruber, 2006, with changes in pool sizes from Sabine et al., 2004a). The net terrestrial loss of –39 GtC is inferred from cumulative fossil fuel emissions minus atmospheric increase minus ocean storage. The loss of –140 GtC from the ‘vegetation, soil and detritus’ compartment represents the cumulative emissions from land use change (Houghton, 2003), and requires a terrestrial biosphere sink of 101 GtC (in Sabine et al., given only as ranges of –140 to –80 GtC and 61 to 141 GtC, respectively; other uncertainties given in their Table 1). Net anthropogenic exchanges with the atmosphere are from Column 5 ‘AR4’ in Table 7.1. Gross fluxes generally have uncertainties of more than ±20% but fractional amounts have been retained to achieve overall balance when including estimates in fractions of GtC yr–1 for riverine transport, weathering, deep ocean burial, etc. ‘GPP’ is annual gross (terrestrial) primary production. Atmospheric carbon content and all cumulative fluxes since 1750 are as of end 1994.(From IPCC Fourth Assessment Report, Climate Change 2007 WG1 Assessment Report AR4, Climate Change 2007, Figure 7.3, page 515)

Objectives

This lesson will apply our classroom introduction to production and decomposition as primary chemical transformations that drive the global carbon cycle []. learned in the classroom. students have learned the basic principles of photosynthesis and decomposition and human impacts on the environment. managing

Provide overview: community garden biogeochemistry as a case study of land use change

• Compare and contrast adjacent unmanaged and managed ecosystems

• Map garden and adjacent land
• Estimate percent cover of each species in each plot
• Estimate percent cover in 10 x 10 m2 plots around the garden
• Measure soil temp and moisture

Materials

10 m or longer Measuring Tape or wheel Map of garden and surrounding area with 10 x 10 m aligned to one corner of garden (add link to pdf here)

Methods

Each group will map entire garden

Homework assignment

Enter x,y coordinate data of sample locations and values of temperature and moisture. Write for 15 minutes about the plot without editing and then summarize in one paragraph.