When you summarize or paraphrase someone else's information in several sentences or more, it feels awkward to put in a citation at the end of each sentence you write. It is also awkward to read! However, technically, APA demands that your reader knows exactly what information you got from someone else and when you start using it. Thus, an end-of-paragraph citation does not meet that requirement.
Solution: Use a lead-in at the beginning of your paragraph. Basically, introduce the source you are summarizing or paraphrasing at the beginning of the paragraph. Then, refer back to the source when needed to ensure your reader understands you are still using the same source.
For examples of the "bad," the "ugly," and the "good," please see below:
Bad. In this paragraph, the citation occurs only at the end, and the reader does not know exactly when/where information comes from the source. Do not do this:
Frogs are excellent indicator species to measure wetland health. They are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. When frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. When oddities in frog morphology appear, like frogs with five legs or two heads, one can assume something is going wrong in the wetland environment (Willemssen, 2010).
Correct, but Ugly. This paragraph is technically correct for APA, but it is difficult to read in large part because the in-text citations are intrusive and awkward :
Frogs are excellent indicator species to measure wetland health. They are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution (Willemssen, 2010). When frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland (Willemssen, 2010). When oddities in frog morphology appear, like frogs with five legs or two heads, one can also assume something is going wrong in the wetland environment (Willemssen, 2010).
Good. These paragraphs are "APA correct" and easy to read. Note the reader knows exactly when/where information from the source is used:
Frogs are excellent indicator species to measure wetland health. According to a recent study by Willemssen (2010), frogs are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. The study notes that when frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. When oddities in frog morphology appear, like frogs with five legs or two heads, one can assume something is going wrong in the wetland environment (Willemssen, 2010).
Frogs are excellent indicator species to measure wetland health. Willemssen (2010) relates to research conducted recently in Wisconsin that shows that frogs are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. Her research indicates that when frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. Also, she finishes by noting that when oddities in frog morphology appear, like frogs with five legs or two heads, one can also assume something is going wrong in the wetland environment.
Frogs are excellent indicator species to measure wetland health. Willemssen (2010) recently conducted research in Wisconsin that shows that frogs are very sensitive to changes in pH caused by acid rain, and they are also very sensitive to different types of pollution. Willemssen's research indicates that when frog populations in a wetland plummet, one can be sure that something is going wrong in the wetland. One very telling quote from Willemssen's research is that "87% of wetlands where two-headed frogs are found have high levels of environmental contamination" (p. 341).